The Collaborative International Dictionary of English v.0.48:

Breach \Breach\ (br[=e]ch), 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.
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   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.
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   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.
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            Once more unto the breach, dear friends, once more;
            Or close the wall up with our English dead. --Shak.
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   4. A breaking of waters, as over a vessel; the waters
      themselves; surge; surf.
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            The Lord hath broken forth upon mine enemies before
            me, as the breach of waters.          --2 Sam. v.
                                                  20.
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   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.
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   5. A breaking up of amicable relations; rupture.
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            There's fallen between him and my lord
            An unkind breach.                     --Shak.
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   6. A bruise; a wound.
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            Breach for breach, eye for eye.       --Lev. xxiv.
                                                  20.
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   7. (Med.) A hernia; a rupture.
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   8. A breaking out upon; an assault.
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            The Lord had made a breach upon Uzza. --1. Chron.
                                                  xiii. 11.
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   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.
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   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.
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   Syn: Rent; cleft; chasm; rift; aperture; gap; break;
        disruption; fracture; rupture; infraction; infringement;
        violation; quarrel; dispute; contention; difference;
        misunderstanding.
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WordNet (r) 3.0 (2006):

breach of trust
    n 1: violation (either through fraud or negligence) by a trustee
         of a duty that equity requires of him

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

BREACH OF TRUST. The willful misappropriation, by a trustee, of a thing which
had been lawfully delivered to him in confidence.
     2. The distinction between larceny and a breach of trust is to be found
chiefly in the terms or way in which the thing was taken originally into the
party's possession; and the rule seems to be, that whenever the article is
obtained upon a fair contract, not for a mere temporary purpose, or by one
who is in the. employment of the deliverer, then the subsequent
misappropriation is to be considered as an act of breach of trust. This rule
is, however, subject to many nice distinctions. 15 S. & R. 93, 97. It has
been adjudged that when the owner of goods parts with the possession for a
particular purpose, and the person who receives them avowedly for that
purpose, has at the time a fraudulent intention to make use of the
possession as the weans of converting the goods to his own use, and does so
convert them, it is larceny; but if the owner part with the property,
although fraudulent means have been used to obtain it, the, act of
conversion is not larceny. Id. Alis. Princ. c. 12, p. 354.
     3. In the Year Book, 21 H. VII. 14, the distinction is thus stated:
Pigot. If I deliver a jewel or money to my servant to keep, and he flees or
goes from me with the jewel, is it felony ? Cutler said, Yes : for so long
as he is with me or in my house, that which I have delivered to him is
adjudged to be in my possession; as my butler, who has my plate in keeping,
if he flees with it, it is felony. Same law; if he who keeps my horse goes
away with, him: The reason is, they are always in my possession. But if I
deliver a horse to my servant to ride to market or the fair and he flee with
him, it is no felony; for e comes lawfully to the possession of the horse by
delivery. And so it is, if I give him a jewel to carry to London, or to pay
one, or to buy a thing, and he flee with it, it is not felony : for it is
out of my possession, and he comes lawfully to it. Pigot. It can well be:
for the master in these cases has an action against him, viz., Detinue, or
Account. See this point fully discussed in Stamf. P. C. lib. 1; Larceny, c.
15, p. 25. Also, 13 Ed. IV. fo. 9; 52 H. III. 7; 21 H. VII. 15.