The Collaborative International Dictionary of English v.0.48:

committed \committed\ adj.
   1. Bound or obligated, as under a pledge to a particular
      cause, action, or attitude. Opposite of uncommitted.

   Note: [Narrower terms: bound up, involved, wrapped up;
         dedicated, devoted; pledged, sworn]
         [WordNet 1.5]

   2. Associated in an exclusive sexual relationship; also
      called attached. Opposite of unattached.

   Note: [Narrower terms: affianced, bespoken, betrothed,
         engaged, pledged, promised(predicate); married]
         [Also See: loving.]

   Syn: attached.
        [WordNet 1.5]

   3. Consigned involuntarily to custody, as in a prison or
      mental institution.
      [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Betroth \Be*troth"\, v. t. [imp. & p. p. Betrothed; p. pr. &
   vb. n. Betrothing.] [Pref. be- + troth, i. e., truth. See
   Truth.]
   1. To contract to any one for a marriage; to engage or
      promise in order to marriage; to affiance; -- used esp. of
      a woman.
      [1913 Webster]

            He, in the first flower of my freshest age,
            Betrothed me unto the only heir.      --Spenser.
      [1913 Webster]

            Ay, and we are betrothed.             --Shak.
      [1913 Webster]

   2. To promise to take (as a future spouse); to plight one's
      troth to.
      [1913 Webster]

            What man is there that hath betrothed a wife, and
            hath not taken her?                   --Deut. xx. 7.
      [1913 Webster]

   3. To nominate to a bishopric, in order to consecration.
      --Ayliffe.
      [1913 Webster]

WordNet (r) 3.0 (2006):

betrothed
    adj 1: pledged to be married; "the engaged couple" [syn:
           bespoken, betrothed]
    n 1: the person to whom you are engaged

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "betrothed":
   affianced, assured, bound, bride-to-be, committed, compromised,
   contracted, engaged, fiance, fiancee, future, guaranteed, intended,
   obligated, pledged, plighted, promised, sworn, underwritten,
   warranted