The Collaborative International Dictionary of English v.0.48:

Deleterious \Del`e*te"ri*ous\, a. [LL. deleterius noxious, Gr.
   dhlhth`rios, fr. dhlei^sqai to hurt, damage; prob. akin to L.
   delere to destroy.]
   Hurtful; noxious; destructive; pernicious; as, a deleterious
   plant or quality; a deleterious example. --
   Del`e*te"ri*ous*ly, adv. -- Del`e*te"ri*ous*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

deleterious
    adj 1: harmful to living things; "deleterious chemical
           additives" [syn: deleterious, hurtful, injurious]

Moby Thesaurus II by Grady Ward, 1.0:

46 Moby Thesaurus words for "deleterious":
   baleful, baneful, corroding, corrosive, corrupting, corruptive,
   counterproductive, damaging, deadly, destroying, destructive,
   detrimental, disadvantageous, disserviceable, distressing, harmful,
   hurtful, injurious, lethal, malefic, malevolent, malign, malignant,
   mischievous, noisome, noxious, ominous, pernicious, poisonous,
   prejudicial, ruining, ruinous, scatheful, toxic, unadvantageous,
   unfavorable, unprofitable, unrewarding, useless, venenate,
   veneniferous, venenous, venomous, vicious, virulent, worthless