Appendix:Latin third declension

Third Declension

 * Parisyllabic, nouns that have an equal number of syllables in the nominative and in the genitive singular (e.g. nom. civis, gen. civis).
 * Imparisyllables, nouns that do not have an equal number of syllables in the nominative and in the genitive singular (e.g. nom. consul, gen. consulis).
 * In some "imparisyllabic" the genitive plural ends in "ium": lis, litis; dos, dotis; mus, muris; etc.
 * In some cases the accusative singular ends in "-im" and the ablative singular in "-i": turris,-is; puppis, -is; sitis, -is; vis, -is; tussis, -is; securis, -is; febris, -is.
 * "Animal, -is"; "calcar,-is" and other neuter nouns that end in "-al/-ar" are considered as parisyllables.

Description
Latin nouns of the third declension comprise consonant stems and i-stems (e.g., as the i in the neuter genitive plural animalium). They are of all three genders, and have genitives in -is. The forms of the nominative and vocative singular are identical to each other and are often quite different from other cases, in which case both stems are given in citation forms.

Words borrowed from Greek's third declension are inflected with a varying mixture of Greek and Latin case endings.

Consonant stem
Citation form: , hominis

Neuter consonant stem
Citation form: , nōminis

i-stem
Citation form: turris, turris

"Pure" i-stem
Citation form: animal, animālis

Mixed declension (mixed i-stem)
Citation form: nox, noctis

Declesion general
Citation form: āēr, āeris m, sometimes f

Citation form: tigris, tigridis m and f

Similiar to i-stem declension:

Examples:
 * haeresis, -eos, f.; basis, -is and -eos, f.;  tigris, -is, m. and f.

For feminine proper nouns from Greek in -ō with genitive in -ūs, see Appendix:Latin fourth declension § Feminine -ō form (from Greek).

five types of Greek nouns third declension
Excluding proper nouns, there seem to be around 4-5 types of declensions of greek nouns as part of Latin's 3rd declension: There are 3 declension variants: 1. more like Greek declension; 2. influenced by Latin's second declension and 3. changed to masculine words like Latin's second declension (e.g. cētus, -i, m. from cētos, -us, n. = (τό) κῆτος). Examples:
 * 1. in -ō, like ēchō, -ūs, f.:
 * Gen. sg. -ûs, all other singular cases -ô. Plural isn't mentioned in the sources above, thus should be regular (e.g. êchês in nom.pl.)
 * echo is said to be in 3rd declension - not in 4 as it's here at Wiktionary.
 * Georges mentions acc. sg as -ōn for êchô.
 * Like Dîdô it might also be -onis, -onî, -onem, -one (gen., dat., acc., abl. sg.).
 * Maybe some of these words were adopted like Latin words in -o, -onis, f.
 * 2. chaos, epos, melos - n.:
 * It's commonly said that some cases are missing or were missing in antique times.
 * 3. chelys (f.):
 * It is similar to the variant that is similar to i-stem declension (see below), but often without i, e.g.: acc.sg. as -n instead of -in added to chely-, or acc.sg. as -yn instead of -in added to chel-.
 * Instead of e.g. -ibus in dat.&abl. pl. it might also be chelybus (Lewis Marcus).
 * Somewhere forms like chelin instead of chelyn were mentioned.
 * 4. Like i-declension:
 * Vowel lengths: Gen. sg.: In older English works (A&G, L&S) it is -eōs instead of -eos. Allen & Greenough and Lewis & Short have -eōs; Lewis Marcus, Georges, Pons have -eos. As Georges and Pons are newer than A&G and L&S, it seems more reliable (cf. stēlla, as opposed to stella).
 * Examples: haeresis, basis (acc. pl. also -e͡is and accourding to Lewis Marcus with other irregular forms), tigris (gen. sg. -is), poēsis (poësis)
 * 5. Like consonantic declension:
 * ‡¹ (especially) by words with gen. sg. in dis it is also dos
 * ‡² a) Accourding to Lewis Marcus some words have the ending is resp. -isi and -ibus, e.g. heroisi from heros. b) Weyh writes that dat. pl. can be -si and -sin (example: ethesi), and Georges and Lewis & Short have abl. pl. ethesin of ēthos. "herosi" can be found, it's e.g. in Prisciani Caesariensis Grammatici Opera ("non herosi [...] herosi"). c) ἥρως is like herosi[n] in dat. pl. Thus -si[n] in dat. and abl. pl. makes sense, but heroisi seems wrong. -- Maybe pure Greek declensions (in singular and plural) + (old) transcription into Latin should be added, so one can see what might be possible. (?)
 * ‡³ (at least) some words have -es and -ēs/-as
 * Words of neuter gender have forms of the 3rd and of the 2nd declension in plural. Well, poēma/poëma has those forms, but that could also be an exception.
 * hērōs, adamās (also adamāns), lebēs (Greek-like acc. pl. with -es and -as)
 * lampas (Greek-like acc. pl. with -es and -as), tigris (-idis; having the forms of tigris, -is in gen. sg. and nom., gen., dat. and abl. pl.), delphīn (also delphīs)
 * pēlamys, chlamys
 * crāter, āēr
 * poēma (poëma), n.

Description
Latin nouns of the third declension comprise consonant stems and i-stems. The consonant stems include the comparative form of adjectives. This declension is divided into three subcategories: adjectives of one termination (which includes present participles), adjectives of two terminations (one for  and, and one for ), and adjectives of three terminations (which are generally -er , -ris  and -re ).

One-termination consonant stem
Citation form: vetus, -eris

One-termination i-stem
Citation form: atrōx, -ōcis

Two-termination consonant stem (comparatives)
Citation form: melior, -us

Two-termination i-stem
Citation form: tristis, -e