# Esperanto word building: roots, affixes, compounds

Source: https://esperantopedia.org/grammar/word-building/
Language: en
Updated: 2026-10-28

> Esperanto builds words from unchanging parts: mal·san·ul·ej·o means hospital. How roots, endings, affixes and compounds turn one root into a word family.

Esperanto words are built from **parts that never change shape**: a root, optional prefixes and suffixes, and a grammatical ending. *Mal·san·ul·ej·o* is "opposite + healthy + person + place + noun", which means "hospital". Once you know the parts, you can take a word apart – and build new ones.

malsanulejo = hospital | san = healthy

This is why Esperanto needs fewer roots than other languages. Zamenhof's first textbook, the *Unua Libro* (1887), had only 917 roots. With endings, affixes and compounding, each root produces a family of related words.

**One root, dozens of words** Reta Vortaro lists 23 words built on the root san-. Here are 15 of them – know a few prefixes and suffixes and you understand them without a dictionary. Word families: Reta Vortaro (GPL); structure: Esperantopedia's analyser; meanings: Esperantopedia, Wiktionary, ReVo.

lernejestro = head teacher | lern = learn | bel = beautiful | dom = house
resaniĝi = to recover | san = healthy
gepatroj = parents | patr = father

## Four kinds of building blocks

| Block | Closed or open | How many | Examples |
|---|---|---|---|
| Roots | open | 4,953 official elements in the Academy's dictionary, plus 420 roots added in 2023 | *dom-, kur-, bel-* |
| Endings | closed | 11 | *-o, -a, -e, -i, -as, -is, -os, -us, -u, -j, -n* |
| Affixes | closed | 10 [prefixes](https://esperantopedia.org/grammar/prefixes/), 31 [suffixes](https://esperantopedia.org/grammar/suffixes/), 6 participle suffixes | *mal-, -ej-, -ant-* |
| Small words without endings | closed | 184 in the Academy's dictionary | *la, kaj, sur, ankaŭ* |

The Academy's dictionary (*Akademia Vortaro*) counts 4,953 official elements. That figure includes the 11 endings and 184 small words; the rest need an ending. The 10th Official Addition of 2023 added 420 new roots.

## Endings decide the word class

The same root becomes a noun, adjective, adverb or verb just by changing the ending. See [nouns and adjectives](https://esperantopedia.org/grammar/nouns-adjectives/) and [verbs](https://esperantopedia.org/grammar/verbs/).

| Ending | Word class | *rapid-* | *san-* |
|---|---|---|---|
| *-o* | noun | *rapido* "speed" | *sano* "health" |
| *-a* | adjective | *rapida* "fast" | *sana* "healthy" |
| *-e* | adverb | *rapide* "quickly" | *sane* "healthily" |
| *-i* | verb | *rapidi* "to hurry" | *sani* "to be healthy" |

Each root has a basic meaning of its own: an action, a quality or a thing. The *-o* form shows it (PMEG). *Kombi* "to comb" is an action, so the comb is *kombilo* "combing tool". *Broso* "brush" is a thing, so brushing is simply *brosi*.

## Affixes add meaning

Prefixes come before the root, suffixes after it. Each adds one meaning: *mal-* "opposite", *-ej-* "place", *-ul-* "person", *-in-* "female", *-et-* "small", *-eg-* "big", *-ig-* "make", *-iĝ-* "become".

Affixes are also ordinary roots. *Ejo* means "place", *ilo* "tool", *eta* "tiny", *ege* "very", *ree* "again".

## A word family: lern- "learn"

| Word | Parts | Meaning |
|---|---|---|
| *lerni* | lern·i | to learn |
| *lernanto* | lern·ant·o | pupil, learner |
| *lernejo* | lern·ej·o | school |
| *lernejano* | lern·ej·an·o | school student |
| *lernejestro* | lern·ej·estr·o | head teacher |
| *lernolibro* | lern·o·libr·o | textbook |
| *lernema* | lern·em·a | eager to learn |
| *lernebla* | lern·ebl·a | learnable |
| *lernado* | lern·ad·o | studying, the learning process |
| *ellerni* | el·lern·i | to learn thoroughly, master |
| *relerni* | re·lern·i | to learn again |
| *memlerninto* | mem·lern·int·o | self-taught person |

A second family, from *san-* "healthy": *sana* "healthy", *malsana* "ill", *malsano* "illness", *malsanulo* "patient", *malsanulejo* "hospital", *sanigi* "to heal", *resaniĝi* "to recover".

## Compounds: the main word comes last

Rule 11 of the Fundamento: compounds are made by joining roots, with the main word last. The front part narrows the meaning of the last part (PMEG).

- *vaporŝipo* – "steamship" (a ship driven by steam); *ŝipvaporo* would be steam from a ship
- *fervojo* – "railway" (literally "iron road")
- *ĉefurbo* – "capital city" (main town)
- *dikfingro* – "thumb" (thick finger)

A linking vowel, usually *-o-*, can go between the parts for easier pronunciation or clarity: *lern·o·libr·o*, *sang·o·ruĝ·a* "blood-red". It is usually left out when the front part simply describes the head like an adjective: *dikfingro*, not *dikafingro* (PMEG).

A phrase with a preposition can also become one word. Here the main word is not last: *sen hejmo* "without a home" → *senhejma* "homeless"; *inter nacioj* → *internacia* "international"; *sub tegmento* → *subtegmento* "attic". See [prepositions](https://esperantopedia.org/grammar/prepositions/).

## From 917 roots to tens of thousands of words

The *Unua Libro* of 1887 had 917 roots, and Zamenhof's *Universala Vortaro* (1894) added 1,740 more. The largest dictionary, the *Plena Ilustrita Vortaro*, listed 16,780 entries and 46,890 lexical units in its 2002 edition. Most of these units are derived words and compounds built from a much smaller set of roots.

The Academy recommends the principle of **necessity and sufficiency**, formulated by René de Saussure in 1913. Use every part needed for a clear meaning, and no more. *Sufiĉo* already means "sufficiency", so *sufiĉeco* adds nothing.

## Traps

**1. Fixed meanings.** The parts explain a word but do not define it. *Lernejo* is a school, not any place where someone learns. Other examples: *vortaro* "dictionary" (collection of words), *arbaro* "forest", *vagonaro* "train", *pordego* "gate", *rideti* "to smile", *ŝtrumpeto* "sock". PMEG notes that *ladskatolo* is a tin can, not any tin box.

**2. Words that only look built.** *Kolego* "colleague" is not *kol·eg·o* "huge neck". *Okulo* "eye" is not *ok·ul·o* "eight-person", and *haringo* "herring" is not *har·ing·o*. PMEG counts more than 150 roots in PIV that merely look as if they contain the suffix *-et-*.

**3. -ig- and -iĝ- depend on the root.** *Fermi* "to close (something)" gives *fermiĝi* "to close (by itself)". *Sidi* "to sit" gives *sidigi* "to seat someone" and *sidiĝi* "to sit down". Check in a [dictionary](https://esperantopedia.org/dictionary/) whether a verb takes an object.

**4. -um- has no fixed meaning.** *Kolumo* "collar", *aerumi* "to air out" and *plenumi* "to fulfil" must be learned one by one.

## Examples in sentences

- *Mia fratino lernas en granda lernejo.* – "My sister studies at a big school."
- *La lernantoj demandis la instruiston pri la lernolibro.* – "The pupils asked the teacher about the textbook."
- *Esperanto estas facile lernebla lingvo.* – "Esperanto is an easy language to learn."
- *Mia avo laboris kiel fervojisto.* – "My grandfather worked as a railwayman."
- *Mia dormoĉambro estas malgranda sed hela.* – "My bedroom is small but bright."
- *La vortaro helpas min kompreni novajn vortojn.* – "The dictionary helps me understand new words."
- *Ĉu vi havas tranĉilon por la pano?* – "Do you have a knife for the bread?"
- *Ŝia parolado estis mallonga kaj klara.* – "Her speech was short and clear."
- *Vespere ni hejmeniris piede.* – "In the evening we walked home."

## Common questions

### How many words does Esperanto have?
There is no fixed number, because new words can be built at any time. The largest dictionary, PIV (2002), has 46,890 lexical units; the Academy's official list has 4,953 elements plus 420 roots added in 2023.

### Can I make up new words in Esperanto?
Yes. Any correct combination of parts is grammatical and usually understood. Check a dictionary first, because an established word may already exist with a fixed meaning.

### Why is the main word last in Esperanto compounds?
Rule 11 of the Fundamento puts the main word at the end. The front part only narrows it: *vaporŝipo* is a kind of ship, not a kind of steam.

### What is the linking -o- in words like lernolibro?
It is an optional vowel between two roots that makes the word easier to say or understand. It is the noun ending used as a joint, and it never takes *-j* or *-n*.

### Why does lernejo mean "school" and not any place for learning?
Like words in any language, Esperanto compounds get a fixed, conventional meaning. The parts give a strong hint; the dictionary gives the exact sense.

## Sources

- [Fundamento de Esperanto – grammar in English (rule 11)](https://www.akademio-de-esperanto.org/fundamento/gramatiko_angla.html)
- [Akademio de Esperanto – Akademia Vortaro, explanations and statistics](https://www.akademio-de-esperanto.org/akademia_vortaro/klarigoj.html)
- [Akademio de Esperanto – 10th Official Addition (2023)](https://www.akademio-de-esperanto.org/decidoj/10oa.html)
- [PMEG – Word-building principles](https://bertilow.com/pmeg/vortfarado/principoj/index.html)
- [PMEG – Compounds and front elements](https://bertilow.com/pmeg/vortfarado/principoj/antauelementoj.html)
- [PMEG – Phrase words](https://bertilow.com/pmeg/vortfarado/principoj/frazetvortigo.html)
- [PMEG – Apparent compounds](https://bertilow.com/pmeg/vortfarado/principoj/shajnkunmetajhoj.html)
- [Reta Vortaro – lern/ (word family)](https://reta-vortaro.de/revo/art/lern.html)
- [uea.facila – La Unua Libro (917 roots)](https://uea.facila.org/artikoloj/lingvo/la-unua-libro/)
- [Wikipedia – Esperanto vocabulary](https://en.wikipedia.org/wiki/Esperanto_vocabulary)
- [Wikipedia – Plena Ilustrita Vortaro de Esperanto](https://en.wikipedia.org/wiki/Plena_Ilustrita_Vortaro_de_Esperanto)
- [Vikipedio – Neceso kaj sufiĉo](https://eo.wikipedia.org/wiki/Neceso_kaj_sufi%C4%89o)