from Wiktionary, Creative Commons Attribution/Share-Alike License
- suffix used to indicate a plural form of some words of Latin or Italian origin, such as virtuosi or concerti
- suffix Used to form adjectives and nouns describing people of a particular city, region, or country, and the language spoken by these people.
From Latin -ī, the plural ending of the Latin second declension, whence the plural of Italian nouns in -o and -e. (Wiktionary)
From the Arabic nisba suffix ـي (-ī, -iyy). In English productive from the 19th century. (Wiktionary)