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
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:
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.
Mi vidas leonon. - I see a lion.
The noun leonon is the object here (and therefore has the accusative ending -N).
Ludoviko, donu al mi panon. - Ludoviko, give me bread.
Ludoviko functions as a vocative.
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).
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).
Mi estas muzikisto. - I am a musician.
The nouns muzikisto acts as a predicate description of the subject mi.
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.
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.