Source : Webster's Revised Unabridged Dictionary (1913)

Tacit \Tac"it\, a. [L. tacitus, p. p. of tacere to be silent, to
   pass over in silence; akin to Goth. [thorn]ahan to be silent,
   Icel. [thorn]egja, OHG. dag[=e]n: cf. F. tacite. Cf.
   {Reticent}.]
   Done or made in silence; implied, but not expressed; silent;
   as, tacit consent is consent by silence, or by not
   interposing an objection. -- {Tac"it*ly}, adv.

         The tacit and secret theft of abusing our brother in
         civil contracts.                         --Jer. Taylor.

Source : WordNet®

tacit
     adj : indicated by necessary connotation though not expressed
           directly; "gave silent consent"; "a tacit agreement";
           "the understood provisos of a custody agreement" [syn:
           {implied}, {silent}, {understood}]