quadrinus

Analogous formation after the organic trīnus, from quadri- +‎ -nus, doublet of quaternus.

• (Classical Latin) IPA^(key): [kʷaˈdriː.nʊs]
• (modern Italianate Ecclesiastical) IPA^(key): [kʷaˈd̪riː.nus]

quadrīnus (feminine quadrīna, neuter quadrīnum); first/second-declension numeral

1. (in the plural) four each
2. quadruple
3. (with pluralibus tantum) four

This is part of the Latin series of distributive numerals. These numerals are inflected as first/second-declension adjectives; in Classical Latin, they typically accompany plural nouns (with which they agree in case and gender) and have the following functions:

• to express the sense “[numeral] [noun]s each/apiece”, as in hominis digiti ternos articulos habent, “a man’s fingers have three joints each” (Pliny the Elder, Natural History 11.244.3).

• to express multiplication after a numeral adverb,^[1] as in Gallinaciis enim pullis bis deni dies opus sunt, pavoninis ter noveni "hens' [eggs] need twice ten days, peahens' thrice nine" (Marcus Terentius Varro, Res Rusticae 3.9.10)

• to express the sense of cardinal numerals when used with pluralia tantum (plural-only nouns) such as castra "camp":^[1] for example, "twelve camps" is expressed by duodēna castra (Pliny the Elder, Natural History 7.105.5). Distributive forms are regularly used in this context for the number 2 and for all numbers greater than 4. For 1, plural-only nouns are used with plural inflected forms of the cardinal ūnus (“one”), as in ūnae scālae "one flight of stairs" (rather than with forms of the distributive numeral singulus). For 3 and 4, plural-only nouns are used with the plural inflected forms of trīnus^[2] and quadrīnus, as in trīna castra "three camps" (rather than with forms of ternus and quaternus, which tend to be used in distributive function^[3]).

These adjectives do not normally occur in the singular.^[4] However, some singular forms are attested in Classical Latin poetry,^[1] possibly motivated by metrical considerations (e.g. corpore bīnō "twofold body" in Lucretius De Rerum Natura 5.879, and bīnus ... honor "double/twofold honor" in Ovid Epistulae ex Ponto 4.9.64). Singular forms are also attested in postclassical Latin, where these adjectives sometimes have non-distributive meanings (taking an ordinal, cardinal, or collective sense instead). These alternative senses are sometimes continued by Romance descendants (e.g. Spanish noveno (“ninth”) from Latin novēnus).

The genitive plural of singulus is usually singulōrum/singulārum, but distributive numerals greater than one commonly use short genitive plural forms ending in -um rather than the longer forms ending in -ōrum and -ārum.^[4][2]

First/second-declension adjective.

• quadrīni in Gaffiot, Félix (1934) Dictionnaire illustré latin-français, Hachette.
• “quadrīni”, in Charlton T. Lewis and Charles Short (1879) A Latin Dictionary, Oxford: Clarendon Press