The Collaborative International Dictionary of English v.0.48:

Acquiescence \Ac`qui*es"cence\, n. [Cf. F. acquiescence.]
   [1913 Webster]
   1. A silent or passive assent or submission, or a submission
      with apparent content; -- distinguished from avowed
      consent on the one hand, and on the other, from opposition
      or open discontent; quiet satisfaction.
      [1913 Webster]

   2. (Crim. Law)
      (a) Submission to an injury by the party injured.
      (b) Tacit concurrence in the action of another. --Wharton.
          [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

147 Moby Thesaurus words for "acquiescence":
   OK, Quakerism, acceptance, acceptation, acception, accession,
   accommodation, accord, accordance, adaptation, adaption,
   adjustment, affirmation, affirmative, affirmative voice,
   agreeability, agreeableness, agreement, agreement in principle,
   alacrity, allegiance, amenability, approbation, approval, ardor,
   assent, assentation, assurance, assuredness, aye, belief, blessing,
   certainty, cheerful consent, complaisance, compliance, concurrence,
   confidence, conformance, conformation other-direction, conformity,
   congruity, connivance, consent, consistency, conventionality,
   cooperativeness, correspondence, credence, credit, credulity,
   deference, dependence, docility, duteousness, dutifulness,
   eagerness, endorsement, enthusiasm, faith, favorable disposition,
   favorableness, fealty, flexibility, forwardness, gameness,
   general agreement, goodwill, harmony, hearty assent, homage, hope,
   humbleness, humility, keeping, kneeling, line, loyalty,
   malleability, meekness, nonopposal, nonopposition, nonresistance,
   nonviolent resistance, obedience, obediency, obeisance, observance,
   okay, orthodoxy, passive resistance, passiveness, passivity,
   permission, pliability, pliancy, promptitude, promptness, quietism,
   ratification, readiness, reception, receptive mood, receptiveness,
   receptivity, reconcilement, reconciliation, reliance, reliance on,
   resignation, resignedness, responsiveness, right mood, sanction,
   service, servility, servitium, stock, store, strictness,
   subjection, submission, submissiveness, submittal,
   suit and service, suit service, supineness, support, sureness,
   surety, suspension of disbelief, tractability, traditionalism,
   trust, uncomplainingness, ungrudgingness, uniformity, unloathness,
   unreluctance, warm assent, welcome, willing ear, willing heart,
   willingness, yielding, zeal, zealousness