From Ancient Greek οἱ (hoi).
οι • (oi) m pl or f pl
1. The final ν is preserved before vowels, and the plosive/affricate consonants: κ, π, τ, ξ, ψ, μπ, ντ, γκ, τσ, τζArchaic forms used in certain fixed phrases: τοις (tois), τας (tas)