Neuter Nouns in -ο | Greek Grammar

If you want an easy win in Greek noun declension, start here. Neuter nouns ending in -ο — το βιβλίο (the book), το νερό (the water), το αυτοκίνητο (the car) — are among the first nouns you meet, and they behave with unusual generosity: three of the four cases look exactly the same. This page shows you the full paradigm, the one form you actually have to learn (the genitive), and the single accent trap that catches learners.

The one thing that makes neuters easy: nom = acc = voc

In Greek, every noun has four cases — nominative (the subject), accusative (the direct object), genitive (possession, "of"), and vocative (calling out to someone). For masculine and feminine nouns those cases often differ, so you have to track which form goes where. Neuters throw that worry out: the nominative, accusative and vocative are always identical, in both the singular and the plural. That's true of every neuter class in the language, not just the -ο one.

The practical upshot: in the singular, only the genitive has its own shape. Learn the nominative, and you already know the accusative and the vocative for free.

Το βιβλίο είναι πάνω στο τραπέζι.

to vivlío íne páno sto trapézi

The book is on the table. (nominative — subject)

Διαβάζω το βιβλίο στο τρένο.

dhiavázo to vivlío sto tréno

I read the book on the train. (accusative — object, same form)

Notice that English does the same thing with word order — "the book" looks identical whether it's the subject or the object. A Greek masculine noun would change (ο φίλος → τον φίλο), but the neuter το βιβλίο stays put. So the neuter is, if anything, closer to how English behaves than the other genders are.

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For any neuter noun, the subject form and the object form are the same word. You only ever change a neuter for the genitive ("of the …") and for the plural. That's two things to learn, not four.

The singular paradigm

The endings are: -ο for nominative / accusative / vocative, and -ου for the genitive. Here is το βιβλίο in full:

Case	Singular	Plural
Nominative	το βιβλίο	τα βιβλία
Genitive	του βιβλίου	των βιβλίων
Accusative	το βιβλίο	τα βιβλία
Vocative	βιβλίο	βιβλία

The article changes with the case just as much as the noun does — το (nom/acc), του (gen sing), τα (nom/acc plural), των (gen plural). Always store a neuter noun with its το, because the article is what tells you the gender.

Η τιμή του βιβλίου είναι δέκα ευρώ.

i timí tu vivlíu íne dhéka evró

The price of the book is ten euros. (genitive singular)

Θέλω ένα ποτήρι νερό, παρακαλώ.

thélo éna potíri neró parakaló

I'd like a glass of water, please.

Το αυτοκίνητό μου δεν παίρνει μπροστά.

to aftokínitó mu dhen pérni brostá

My car won't start.

(That το αυτοκίνητό carries a second accent because the little word μου leans onto it — a separate topic, but don't let the double accent confuse you; the noun is still just αυτοκίνητο.)

The plural: nom/acc -α, genitive -ων

In the plural, neuters in -ο take -α for nominative / accusative / vocative and -ων for the genitive. So το βιβλίο → τα βιβλία, and "of the books" is των βιβλίων.

Έβαλα όλα τα βιβλία μέσα στην τσάντα.

évala óla ta vivlía mésa stin tsánda

I put all the books inside the bag.

Η τιμή των βιβλίων ανέβηκε φέτος.

i timí ton vivlíon anévike fétos

The price of the books went up this year. (genitive plural)

Τα δέντρα στην αυλή έχασαν τα φύλλα τους.

ta dhéndra stin avlí échasan ta fíla tus

The trees in the yard lost their leaves.

Τα νερά της λίμνης είναι κρύα ακόμα και το καλοκαίρι.

ta nerá tis límnis íne kría akóma ke to kalokéri

The lake's waters are cold even in summer.

A tip for English speakers: don't reach for an -s. Greek marks plurality by changing the ending, not by adding a suffix on top — βιβλίο → βιβλία, δέντρο → δέντρα. The -α ending on a neuter noun is a plural, even though the very similar-looking -α on a feminine noun (η ώρα) is a singular. Context and the article (τα vs η) keep them apart.

The accent trap: proparoxytone genitives shift

Here is the one wrinkle. Greek allows a written accent only on one of the last three syllables of a word. Most -ο nouns keep their accent in the same place throughout the paradigm — βιβλίο → βιβλίου → βιβλία → βιβλίων never moves off the ί. But when a word is stressed on the third-from-last syllable (a proparoxytone, like αυτοκίνητο), the learned genitive pulls the accent one step toward the ending:

Case	Singular	Plural
Nominative	το αυτοκίνητο	τα αυτοκίνητα
Genitive	του αυτοκινήτου	των αυτοκινήτων
Accusative	το αυτοκίνητο	τα αυτοκίνητα
Vocative	αυτοκίνητο	αυτοκίνητα

Watch the stressed syllable move: αυτοκίνητο (on -κί-) → αυτοκινήτου / αυτοκινήτων (on -νή-). The nominative and accusative plural (τα αυτοκίνητα) keep the original accent; only the two genitives shift. The same happens with το πρόσωπο → του προσώπου (face/person) and το άτομο → του ατόμου (individual).

Τα φώτα του αυτοκινήτου έμειναν αναμμένα όλη νύχτα.

ta fóta tu aftokinítu éminan anaména óli níchta

The car's lights were left on all night. (accent shifted to -νή-)

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The accent shift is a hallmark of the more formal, learned vocabulary. Honestly, in everyday A1 speech you rarely need the genitive singular of a neuter — you'd more often say "of" with a whole phrase — so don't lose sleep over it. Just recognise that του αυτοκινήτου is correct and του αυτοκίνητου is not.

A quick contrast with the other neuter classes

Neuter -ο is only one of several neuter families. Its close cousins are the -ι nouns (το παιδί, το σπίτι) and the -μα nouns (το πρόβλημα, το όνομα). All three share the golden rule — nom = acc = voc — but they differ in their genitive and plural endings. The -ο class is the plainest of the three, which is exactly why it's the place to start.

Common Mistakes

❌ Ο βιβλίο είναι καινούριος.

o vivlío íne kenúrios

Incorrect — wrong article and adjective agreement; βιβλίο is neuter, not masculine.

✅ Το βιβλίο είναι καινούριο.

to vivlío íne kenúrio

The book is new.

Because the ending -ο can look like a masculine ending to a beginner, learners reach for ο and make the adjective agree as masculine. It's neuter: το βιβλίο, καινούριο.

❌ Διαβάζω το βιβλίου κάθε βράδυ.

dhiavázo to vivlíu káthe vrádhi

Incorrect — the object needs the plain -ο form, not the genitive -ου.

✅ Διαβάζω το βιβλίο κάθε βράδυ.

dhiavázo to vivlío káthe vrádhi

I read the book every evening.

The direct object is the accusative, which for a neuter is identical to the nominative (-ο). Don't swap in the genitive -ου just because the noun isn't the subject.

❌ Έχω δύο αυτοκίνητα, το χρώμα του αυτοκίνητου μ' αρέσει.

ého dhío aftokínita to chróma tu aftokínitu marési

Incorrect — the proparoxytone genitive must shift the accent.

✅ Έχω δύο αυτοκίνητα, το χρώμα του αυτοκινήτου μ' αρέσει.

ého dhío aftokínita to chróma tu aftokinítu marési

I have two cars; I like the colour of the car.

❌ Αγόρασα καινούρια βιβλίες.

aghórasa kenúria vivlíes

Incorrect — the neuter plural is -α, not -ες.

✅ Αγόρασα καινούρια βιβλία.

aghórasa kenúria vivlía

I bought new books.

The -ες plural belongs to feminine and masculine nouns. Neuters in -ο pluralise with -α: βιβλίο → βιβλία, δέντρο → δέντρα, αυτοκίνητο → αυτοκίνητα.

Key Takeaways

Nom = acc = voc, always. In the singular, only the genitive (-ου) is a separate form.
Plural: -α for nom/acc/voc, -ων for the genitive.
Store every neuter noun with το, because the ending -ο alone won't always tell you the gender.
Proparoxytones (αυτοκίνητο, πρόσωπο) shift the accent in the genitive: του αυτοκινήτου, των αυτοκινήτων.
Mark the object with the plain -ο form, not -ου — the accusative equals the nominative.

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