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]

WordNet (r) 3.0 (2006):

acquiescence
    n 1: acceptance without protest
    2: agreement with a statement or proposal to do something; "he
       gave his assent eagerly"; "a murmur of acquiescence from the
       assembly" [syn: assent, acquiescence]

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



Bouvier's Law Dictionary, Revised 6th Ed (1856):

ACQUIESCENCE, contracts. The consent which is impliedly given by one or both
parties, to a proposition, a clause, a condition, a judgment, or to any act
whatever.
    2. When a party is bound to elect between a paramount right and a
testamentary disposition, his acquiescence in a state of things which
indicates an election, when he was aware of his rights will be prima facie
evidence of such election. Vide 2 Ves. Jr. 371; 12 Ves. 136 1 Ves. Jr. 335;
3 P. Wms. 315. 2 Rop. Leg. 439.
    3. The acts of acquiescence which constitute an implied election, must
be decided rather by the circumstances of each case than by any general
principle. 1 Swanst. R. 382, note, and the numerous cases there cited.
    4. Acquiescence in the acts of an agent, or one who has assumed that
character, will be equivalent to an express authority. 2 Bouv. Inst. n.
1309; Kent, Com. 478; Story on Eq. Sec. 255; 4 W. C. C. R. 559; 6 Miss. R.
Sec. 193; 1 John. Cas. 110; 2 John. Cas. 424 Liv. on Ag. 45; Paley on, Ag.
by Lloyd, 41 Pet. R. 69, 81; 12 John. R. 300; 3 Cowen's R. 281; 3 Pick. R.
495, 505; 4 Mason's R. 296. Acquiescence differs from assent. (q.v.)