ungrateful
From LSJ
P. and V. ἀχάριστος (Eur., Hecuba 254), V. δυσχάριστος (Aesch., Fragment).
unremembering: P. and V. ἀμνήμων.
unpleasing: P. and V. ἄχαρις (Plato also Ar.), P. ἀχάριστος; see unpleasant.
odious: P. and V. βαρύς, ἐπίφθονος; see odious.