From Old English 'fǣtt' (fattened), from Proto-Germanic *faitidaz — originally a participle meaning 'having been fattened up.'
Having excess flesh; containing much fat.
From Old English 'fǣtt' (fat, plump), from Proto-Germanic *faitidaz (fattened), from PIE *poid- (to be fat). Originally a past participle — a 'fat' animal was one that had been fattened. Key roots: *poid- (PIE: "to be fat").