Oi Definition
oi
interjection
Used as a greeting or to attract someone's attention.
American Heritage
Webster's New World
pronoun
(south west England) Eye dialect spelling of I.
Wiktionary
suffix
Plural form of -os.
Wiktionary
Origin of Oi
-
From the Ancient Greek -οι (-oi), the second-declension masculine nominative plural case ending — the plural form of -ος (-os); compare the equivalents of the Latin second declension (-us → -ī), with which the Grecian case endings are usually substituted in English words, especially in the plural.
From Wiktionary