phiPronunciation: /fʌɪ/Definition of phi noun the twenty-first letter of the Greek alphabet (Φ, φ), transliterated as ‘ph’ or (in modern Greek) ‘f’. (Phi) [followed by Latin genitive] Astronomy the twenty-first star in a constellation:Phi Eridani symbol (φ) a plane angle. (φ) a polar coordinate. Often coupled with θ (theta).Origin:Greekphi in other Oxford dictionaries Definition of phi in the US English dictionary
