del·e·te·ri·ous 
(dĕl′ĭ-tîrē-əs)
(dĕl′ĭ-tîrē-əs)adj.
Having a harmful effect; injurious: the deleterious effects of smoking.
[From Greek dēlētērios, from dēlētēr, destroyer, from dēleisthai, to harm.]
del′e·teri·ous·ly adv.
del′e·teri·ous·ness n.