-i

-i¹

suffix forming the plural:

1》 of nouns adopted from Latin ending in -us: foci.

2》 of nouns adopted from Italian ending in -e or -o: dilettanti.

Usage

Many nouns derived from a foreign language retain their foreign plural, at least when they first enter English and particularly if they belong to a specialist field. Over time, it is normal for a word in general use to acquire a regular English plural. This may coexist with the foreign plural (e.g. cactus, plural cacti or cactuses) or it may actually oust a foreign plural (octopus, plural octopuses rather than octopodes).

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-i²

suffix forming adjectives from place names in the Near or Middle East: Azerbaijani.

Origin

from Semitic and Indo-Iranian adjective endings.