Entry 1 sense Webster, 1913 Deleterious /dĕlˌ-ət-ĭr'-ē-əs/ · Del·e·te·ri·ous · IPA /ˌdɛ.ləˈtɪɹ.i.əs/ 01 a. Hurtful; noxious; destructive; pernicious; as, a deleterious plant or quality; a deleterious example. 1. Hurtful; noxious; destructive; pernicious; as, a deleterious plant or quality; a deleterious example.