哀 is a bound form (b.f.) meaning 'sorrowful', 'lamenting', or 'tragic'. It cannot stand alone as a word in modern Chinese; instead it appears as the second element in compound words like 悲哀 (bēi'āi, 'sorrowful'), 哀悼 (āidào, 'to mourn'), and 哀伤 (āishāng, 'grieved'). Knowing this pattern helps you recognize 哀 as the sadness root in formal or literary compounds.