~ 1
■ 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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~ 2
■ suffix forming adjectives from place names in the Near or Middle East: Azerbaijani.
Origin
from Semitic and Indo-Iranian adjective endings.