Nouns are the names of things concrete and abstract, people, animals, phenomena, actions, qualities, species, individuals etc. Nouns in Esperanto have an O-ending.
- tablo - table = name of a concrete object (a concrete noun)
- hundo - dog = name of a animal species
- saĝo - wisdom = denotation of a quality
- amo - love = denotation of a feeling
- kuro - the act of running, the run = name of an action
- martelado - hammering = name of a continuous or repetitive action
- Petro - Peter = name of a person
- Jokohamo - Yokahama = name of a city
The noun ending O can be followed by a J-ending for the plural, and the accusative N-ending. It is also possible to have both, but always J before N:
| tabloj | tablon | tablojn |
| hundoj | hundon | hundojn |
You can substitute the noun ending O by an apostrophe, but only if it is not followed by J or N:hund' = hundo, saĝ' = saĝo, am' = amo, kur' = kuro, Jokoham' = Jokohamo
Use of nouns
Nouns, or rather clauses with a noun as its keyword, function mainly as the subject, object, circumstantial complement or vocative, but they can also function as a supplemental description or predicative description of another word:
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La bona virino trankviligis sian soifon. - The good woman quenched her thirst.
The clause la bona virino, acts as the subject and its keyword is the noun virino.
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Mi vidas leonon. - I see a lion.
The noun leonon is the object here (and therefore has the accusative ending -N).
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Ludoviko, donu al mi panon. - Ludoviko, give me bread.
Ludoviko functions as a vocative.
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Sur la fenestro kuŝas krajono kaj plumo. - On the window lies a pencil and a pen.
The noun phrase sur la fenestro acts as a circumstantial complement of location (and therefore has the preposition of location sur).
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La dentoj de leono estas akraj. - The teeth of a lion are sharp.
The noun phrase de leono functions as a possessive supplement to the noun phrase la dentoj (and therefore has the preposition de).
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Mi estas muzikisto. - I am a musician.
The nouns muzikisto acts as a predicate description of the subject mi.
Noun-like particles
Some particles in Esperanto can take on noun-like characteristics in a sentence, but they don't have the O-ending. Some examples are personal pronouns, correlatives ending in U and O, the names of the Esperanto letters of the alphabet, numerals and the particle ambaŭ.
Also adverbs of quantity can act as nouns.
Proper nouns
Fully esperantized proper nouns always have the O-ending: Anno, Petro, Teodoro, Mario... Also non-esperantized proper nouns are considered nouns, but they don't usually have the O-ending: Anna, Peter, Theodore Roosevelt, Marie Curie, Deng Xiaoping With these names one can omit the accusative N-ending, even if its function in the sentence specifically requires that ending. For more detail read the clarification of the N-ending.