The Collaborative International Dictionary of English v.0.48:

Damage \Dam"age\, v. t. [imp. & p. p. Damaged
   (d[a^]m"[asl]jd); p. pr. & vb. n. Damaging
   (d[a^]m"[asl]*j[i^]ng).] [Cf. OF. damagier, domagier. See
   Damage, n.]
   To occasion damage to the soundness, goodness, or value of;
   to hurt; to injure; to impair.
   [1913 Webster]

         He . . . came up to the English admiral and gave him a
         broadside, with which he killed many of his men and
         damaged the ship.                        --Clarendon.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

damaging \damaging\ adj.
   1. causing harm or injury; as, damaging to career and
      reputation.

   Syn: detrimental, detrimental to(predicate), prejudicial,
        prejudicious.
        [WordNet 1.5]

   2. designed or tending to discredit, especially without
      positive or helpful suggestions.

   Syn: negative.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

damaging
    adj 1: (sometimes followed by `to') causing harm or injury;
           "damaging to career and reputation"; "the reporter's
           coverage resulted in prejudicial publicity for the
           defendant" [syn: damaging, detrimental,
           prejudicial, prejudicious]
    2: designed or tending to discredit, especially without positive
       or helpful suggestions; "negative criticism" [syn:
       damaging, negative]

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "damaging":
   bad, baleful, baneful, corroding, corrosive, corrupting,
   corruptive, counterproductive, deadly, deleterious, detrimental,
   disadvantageous, disserviceable, distressing, eroding, erosive,
   evil, harmful, hurtful, injurious, lethal, malefic, malevolent,
   malign, malignant, mischievous, noisome, noxious, ominous,
   pernicious, poisonous, prejudicial, scatheful, toxic, venenate,
   veneniferous, venenous, venomous, vicious, virulent