ideclension

Ideclension, or i-declension (ideclension), is a term used in Latin grammar to describe a small group of nouns traditionally classed as i-stem. In many grammars these nouns are considered a subset of the second declension, distinguished by a genitive singular ending in -ī and by certain patterns of endings in other cases. The class is mainly masculine and feminine, with a smaller number of neuter nouns.

An archetypal i-stem noun is fili-us, son. Its paradigm largely mirrors the standard second declension: nominative filius, genitive filiī, dative filiō, accusative filium, ablative filiō; plural nominative filiī, genitive filiorum, dative filiīs, accusative filios, ablative filiīs. The defining feature is the -i- in the relevant forms that marks its i-stem character.

Use and classification: In modern Latin grammars, i-declension nouns are often treated as part of the second declension rather than as a separate declension. The term is encountered mainly in historical or pedagogical contexts and in some older grammars; in contemporary linguistics the distinction is described in terms of stem formation and inflection patterns rather than as a separate declension.