psi Syllabification: (psi)Pronunciation: /(p)sī/Definition of psi noun 1the twenty-third letter of the Greek alphabet (Ψ, ψ), transliterated as ‘ps.’. (Psi) [followed by Latin genitive] Astronomy the twenty-third star in a constellation:Psi Aquarii 2supposed parapsychological or psychic faculties or phenomena:he turns to anecdotal evidence to prove that psi existspsi in other Oxford dictionaries Definition of psi in the British & World English dictionary
