Source : Webster's Revised Unabridged Dictionary (1913)

Breach \Breach\, n. [OE. breke, breche, AS. brice, gebrice,
   gebrece (in comp.), fr. brecan to break; akin to Dan.
   br[ae]k, MHG. breche, gap, breach. See {Break}, and cf.
   {Brake} (the instrument), {Brack} a break] .
   1. The act of breaking, in a figurative sense.

   2. Specifically: A breaking or infraction of a law, or of any
      obligation or tie; violation; non-fulfillment; as, a
      breach of contract; a breach of promise.

   3. A gap or opening made made by breaking or battering, as in
      a wall or fortification; the space between the parts of a
      solid body rent by violence; a break; a rupture.

            Once more unto the breach, dear friends, once more;
            Or close the wall up with our English dead. --Shak.

   4. A breaking of waters, as over a vessel; the waters
      themselves; surge; surf.

            The Lord hath broken forth upon mine enemies before
            me, as the breach of waters.          --2 Sam. v.
                                                  20?

   {A clear breach} implies that the waves roll over the vessel
      without breaking.

   {A clean breach} implies that everything on deck is swept
      away. --Ham. Nav. Encyc.

   5. A breaking up of amicable relations; rupture.

            There's fallen between him and my lord An unkind
            breach.                               --Shak.

   6. A bruise; a wound.

            Breach for breach, eye for eye.       --Lev. xxiv.
                                                  20?

   7. (Med.) A hernia; a rupture.

   8. A breaking out upon; an assault.

            The Lord had made a breach upon Uzza. --1. Chron.
                                                  xiii. 11?

   {Breach of falth}, a breaking, or a failure to keep, an
      expressed or implied promise; a betrayal of confidence or
      trust.

   {Breach of peace}, disorderly conduct, disturbing the public
      peace.

   {Breach of privilege}, an act or default in violation of the
      privilege or either house of Parliament, of Congress, or
      of a State legislature, as, for instance, by false
      swearing before a committee. --Mozley. Abbott. 

   {Breach of promise}, violation of one's plighted word, esp.
      of a promise to marry.

   {Breach of trust}, violation of one's duty or faith in a
      matter entrusted to one.

   Syn: Rent; cleft; chasm; rift; aperture; gap; break;
        disruption; fracture; rupture; infraction; infringement;
        violation; quarrel; dispute; contention; difference;
        misunderstanding.

Source : WordNet®

breach of trust
     n : violation (either through fraud or negligence) by a trustee
         of a duty that equity requires of him