Ending system by declension
To put a noun or adjective into the Genitivus pluralis form, one must isolate its practical stem (by dropping the genitive singular ending) and attach the ending corresponding to the declension type.
| Declension | Ending | Examples (Latin and translation) |
|---|---|---|
| I | -ārum | costārum (of ribs), latārum (of wide ones) |
| II (m, n) | -ōrum | sulcōrum (of sulci), ligamentōrum (of ligaments) |
| III | -um or -ium | pulmonum (of lungs), foraminum (of foramina) |
| IV (m, n) | -uum | arcuum (of arches), cornuum (of horns) |
| V | -ērum | faciērum (of surfaces) |
Examples of forming forms from dictionary units
To avoid mistakes when choosing an ending, always base your choice on the dictionary form of the term. It is what indicates the gender and declension number.
- 1st declension: spine (spina, ae f) — spinārum; cheek (bucca, ae f) — buccārum; gingiva (gingiva, ae f) — gingivārum.
- 2nd declension: ventricle (ventriculus, i m) — ventriculōrum; atrium (atrium, i n) — atriōrum; node (nodus, i m) — nodōrum; angle (angulus, i m) — angulōrum; muscle (musculus, i m) — musculōrum; ganglion (ganglion, i n) — gangliōrum.
- 3rd declension: joint (articulatio, onis f) — articulationum; tendon (tendo, inis m) — tendinum.
- 4th declension: sinus (sinus, us m) — sinuum; process (processus, us m) — processuum; knee (genu, us n) — genuum; plexus (plexus, us m) — plexuum.
Grammatical notes and exceptions
Medical Latin abounds with historical exceptions that require separate memorization:
- Vessel (vas, vasis n). In the singular, this word behaves like a mixed-type noun of the 3rd declension. However, in the plural, it completely shifts to the 2nd declension (like the word septum). Accordingly, its Genitive plural form is vasōrum.
- Ilium (os ilium). Students often try to change the word ilium to ilii, thinking it is a 2nd declension singular form. This is a gross error. The word ilium is already the ready-made Genitivus pluralis form of the noun ile, is n (lower abdomen, groin). Its nominative plural is ilia ("flanks"). It is only correct to write os ilium.
- Fauces (fauces, ium). This anatomical term is used exclusively in the plural.
- Greek terms ending in -nx. Words such as larynx (larynx), pharynx (pharynx), meninx (meninx), and phalanx (phalanx) belong to the consonant type rather than the mixed type. Therefore, in the Gen. pl. they take the ending -um: laryngum, pharyngum, meningum, phalangum.
Briefly: answers to topical questions
How to choose between the endings -um and -ium for 3rd declension nouns in the Genitivus pluralis?
There is no general rule for choosing between the endings -um and -ium, but a specific case is described for Greek nouns ending in -nx. In the genitive plural, they end in -um because they belong to consonant stems rather than mixed ones. Such terms include:
- Larynx (larynx) — form laryngum.
- Pharynx (pharynx) — form pharyngum.
- Meninx (meninx) — form meningum.
- Phalanx (phalanx) — form phalangum.
Which Latin anatomical terms are used only in the plural (pluralia tantum)?
In Latin terminology, there are words that are used exclusively in the plural. Such anatomical terms include:
- Fauces (fauces, ium) — a noun that has no singular form.
- Lumbars (lumbi, ōrum m) — a term used only in the plural.
In addition, the pharmaceutical term species (species, ērum f), belonging to the 5th declension, has a similar grammatical property.
It is easy to remember the basic endings of vowel declensions: the first letter of the alphabet gives -ārum (1st decl.), the letter O gives -ōrum (2nd decl.), the letter E gives -ērum (5th decl.), and U is doubled to give -uum (4th decl.).
Class and exam questions
How does the word vas (vessel) decline in the plural?
In the singular, it declines according to the 3rd declension, but in the plural, it paradoxically shifts to the 2nd declension. Therefore, the Genitivus pluralis form appears as vasōrum.
Is it correct to say os ilii for the ilium?
No, this is an error. The word ilium in this expression is already in the genitive plural form of the noun ile (groin). The correct term is only os ilium.
What ending do Greek words in -nx take in the genitive plural?
They end in -um (e.g., pharyngum, phalangum) because grammatically they belong to the consonant type of the 3rd declension.
What else to study on this topic
- Rules for choosing between -um and -ium endings in the 3rd declension
- Pluralia tantum in anatomical terminology
- Algorithm for isolating the practical stem of a word before attaching an ending
- Features of declension of Greek nouns in Latin
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