A termination of Latin and Greek nouns [= i- , ι-, stem or connecting vowel + -a suffix¹ 1] , in Greek esp. frequent as the ending of abstract nouns from adjectives in -ος, etc. Many words so formed are in English use, as hydrophobia, mania, militia; hence frequent in modern Latin terms of Pathology (cephalalgia, hæmaturia, hyperalgia, hysteria); of Botany, in names of classes, orders, or other divisions, as Monandria, Digynia, Cryptogamia, and in generic names of plants, formed on personal names, or otherwise derived, as Dahlia, Fuchsia, Lobelia, Wisteria, Woodsia; Calceolaria, Mantisia, etc.; in names of countries, as Australia, Tasmania, Rhodesia; and in names of alkaloids (after ammonia), as aconitia, atropia, conia, morphia, strychnia, in which more recent nomenclature prefers the ending -ine. In French -ia became -ie, whence Middle English -ie, English -y, in nouns in -ency, -ography, -ology, etc.

Forming plurals of Latin and Greek nouns in -ium, -e (-i), -ιον, some of which are in English use, as paraphernalia, regalia, saturnalia; hence frequent in modern Latin names of classes, etc. in Zoology, as Mammalia, Marsupialia, Reptilia, Amphibia.