In terms of the usual interpretation of the question (what languages did Greek borrow words from), at different times Greek has borrowed words from:
- Persian (a small number)
- Latin (a fair few)
- Slavonic (surprisingly few)
- Albanian (surprisingly fewer)
- Aromanian (ditto)
- Catalan (one word, παρέα < pare(j)a)
- Romany (very few, although it is the go-to source for cants (secrecy languages), including Kaliarda, the gay cant: Roz Mov – Kaliarda
- Old French (Cypriot)
- Italian and Venetian (lots, though they have been purged)
- (Ottoman) Turkish (lots, though they have been substantially purged)
- French (before World War II)
- English (after World War II)
- … oh, and Ancient Greek
- Can’t think of any words from Aromanian, but there should be a couple
Dialects outside of Greece have borrowed from the majority languages: Calabrian and Salentino in Southern Italy, French in Corsica, Russian and Tatar in Eastern Ukraine (formerly Crimea). And of course languages in the diaspora do the same.