The Collaborative International Dictionary of English v.0.48:

Connivance \Con*niv"ance\, n. [Cf. F. connivence, L.
   conniventia.]
   1. Intentional failure or forbearance to discover a fault or
      wrongdoing; voluntary oversight; passive consent or
      cooperation.
      [1913 Webster]

   2. (Law) Corrupt or guilty assent to wrongdoing, not
      involving actual participation in, but knowledge of, and
      failure to prevent or oppose it.

   Syn: See Collusion.
        [1913 Webster]

WordNet (r) 3.0 (2006):

connivance
    n 1: agreement on a secret plot [syn: connivance, collusion]
    2: (law) tacit approval of someone's wrongdoing [syn:
       connivance, secret approval, tacit consent]

Moby Thesaurus II by Grady Ward, 1.0:

82 Moby Thesaurus words for "connivance":
   OK, acceptance, accord, acquiescence, affirmation, affirmative,
   affirmative voice, agreement, approbation, approval, artifice,
   assent, aye, blessing, cabal, chicane, chicanery, collusion,
   compliance, complicity, complot, confederacy, connivery, consent,
   conspiracy, contrivance, contriving, counterplot, covin,
   deep-laid plot, dodgery, eagerness, endorsement, engineering,
   finagling, finesse, foul play, frame-up, game, indulgence,
   intrigue, little game, machination, maneuvering, manipulation,
   okay, overlooking, permission, permissiveness, pettifoggery,
   pettifogging, plot, plotting, promptitude, promptness,
   ratification, readiness, rigging, sanction, scheme, schemery,
   scheming, sharp practice, skulduggery, sleight, stratagem,
   submission, sufferance, supercherie, tolerance, toleration, trick,
   trickery, underhand dealing, underplot, ungrudgingness,
   unloathness, unreluctance, web of intrigue, willingness, winking,
   wire-pulling



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

CONNIVANCE. An agreement or consent, indirectly given, that something
unlawful shall be done by another.
     2. The connivance of the husband to his wife's prostitution deprives
him of the right of obtaining a divorce; or of recovering damages from the
seducer. 4 T. R. 657. It may be satisfactorily proved by implication.
     3. Connivance differs from condonation, (q.v.) though either may have
the same legal consequences. Connivance necessarily involves criminality on
the part of the individual who connives, condonation may take place without
implying the slightest blame to the party who forgives the injury.
     4. Connivance must be the act of the mind before the offence has been
committed; condonation is the result of a determination to forgive an injury
which was not known until after it was inflicted. 3 Hagg. Eccl. R. 350.
     5. Connivance differs, also, from collusion (q. Y.); the former is
generally collusion. for a particular purpose, while the latter may exist
without connivance. 3 Hagg, Eccl. R. 130. Vide Shelf. on Mar. & Div. 449; 3
Hagg. R. 82; 2 Hagg. R. 376; Id. 278; 3 Hagg. R. 58, 107, 119, 131, 312; 3
Pick. R. 299; 2 Caines, 219; Anth. N.P. 196.