The Collaborative International Dictionary of English v.0.48:

Forget \For*get"\, v. t. [imp. Forgot(Forgat, Obs.); p. p.
   Forgotten, Forgot; p. pr. & vb. n. Forgetting.] [OE.
   forgeten, foryeten, AS. forgietan, forgitan; pref. for- +
   gietan, gitan (only in comp.), to get; cf. D. vergeten, G.
   vergessen, Sw. f["o]rg[aum]ta, Dan. forgiette. See For-,
   and Get, v. t.]
   1. To lose the remembrance of; to let go from the memory; to
      cease to have in mind; not to think of; also, to lose the
      power of; to cease from doing.
      [1913 Webster]

            Bless the Lord, O my soul, and forget not all his
            benefits.                             --Ps. ciii. 2.
      [1913 Webster]

            Let my right hand forget her cunning. --Ps. cxxxvii.
                                                  5.
      [1913 Webster]

            Hath thy knee forget to bow?          --Shak.
      [1913 Webster]

   2. To treat with inattention or disregard; to slight; to
      neglect.
      [1913 Webster]

            Can a woman forget her sucking child? . . . Yes,
            they may forget, yet will I not forget thee. --Is.
                                                  xlix. 15.
      [1913 Webster]

   To forget one's self.
      (a) To become unmindful of one's own personality; to be
          lost in thought.
      (b) To be entirely unselfish.
      (c) To be guilty of what is unworthy of one; to lose one's
          dignity, temper, or self-control.
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Forgotten \For*got"ten\,
   p. p. of Forget.
   [1913 Webster]

WordNet (r) 3.0 (2006):

forgotten
    adj 1: not noticed inadvertently; "her aching muscles forgotten
           she danced all night"; "he was scolded for his forgotten
           chores" [syn: disregarded, forgotten]

Moby Thesaurus II by Grady Ward, 1.0:

71 Moby Thesaurus words for "forgotten":
   absolved, acquitted, ago, antiquated, antique, blotted, blown over,
   by, bygone, bypast, canceled, condoned, dated, dead,
   dead and buried, deceased, defunct, departed, disregarded, elapsed,
   exculpated, excused, exonerated, expired, extinct, finished,
   forgiven, gone, gone glimmering, gone-by, has-been, ignored,
   ill-requited, ill-rewarded, indulged, irrecoverable, lapsed, lost,
   misremembered, neglected, no more, obliterated, obsolete, over,
   overlooked, pardoned, passe, passed, passed away, past,
   past recall, redeemed, remitted, reprieved, run out, shriven,
   spared, unacknowledged, unavenged, uncondemned, uncredited,
   unfairly neglected, unrecognized, unrequited, unresented,
   unrevenged, unrewarded, unthanked, vanished, wiped away,
   wound up