The Collaborative International Dictionary of English v.0.48:

Obligate \Ob"li*gate\, v. t. [imp. & p. p. Obligated; p. pr. &
   vb. n. Obligating.] [L. obligatus, p. p. of obligare. See
   Oblige.]
   1. To bring or place under obligation, moral or legal; to
      hold by a constraining motive. "Obligated by a sense of
      duty." --Proudfit.
      [1913 Webster]

            That's your true plan -- to obligate
            The present ministers of state.       --Churchill.
      [1913 Webster]

   2. To bind or firmly hold to an act; to compel; to constrain;
      to bind to any act of duty or courtesy by a formal pledge.
      [1913 Webster]

            That they may not incline or be obligated to any
            vile or lowly occupations.            --Landor.
      [1913 Webster]

WordNet (r) 3.0 (2006):

obligate
    adj 1: restricted to a particular condition of life; "an
           obligate anaerobe can survive only in the absence of
           oxygen" [ant: facultative]
    v 1: force somebody to do something; "We compel all students to
         fill out this form" [syn: compel, oblige, obligate]
    2: commit in order to fulfill an obligation; "obligate money"
    3: bind by an obligation; cause to be indebted; "He's held by a
       contract"; "I'll hold you by your promise" [syn: oblige,
       bind, hold, obligate]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "obligate":
   accept obligation, agree to, answer for, be answerable for,
   be responsible for, be security for, bind, commit, compel,
   constrain, contract, engage, force, go bail for,
   have an understanding, make imperative, make incumbent, oblige,
   pledge, require, saddle with, shake hands on, take the vows, tie,
   undertake