ἀγὼν πρόφασιν οὐκ ἐπιδέχεται οὐδὲ φιλία → no excuse is allowed by a contest or by a friendship
P. and V. δυσμενής, δύσνους, Ar. and P. κακόνους, V. κακόφρων.
faithless: P. and V. ἄπιστος.