deleterious UK /ˌdɛl.ɪˈtɪə̯.ɹi.əs/US /ˌdɛ.ləˈtɪɹ.i.əs/ adjective2 •Having lower fitness. •(formal) Harmful, often in a subtle or unexpected way.deleterious effects formsmore deleterious · most deleterious
