The Collaborative International Dictionary of English v.0.48:

Detention \De*ten"tion\, n. [L. detentio: cf. F. d['e]tention.
   See Detain.]
   1. The act of detaining or keeping back; a withholding.
      [1913 Webster]

   2. The state of being detained (stopped or hindered); delay
      from necessity.
      [1913 Webster]

   3. Confinement; restraint; custody.
      [1913 Webster]

            The archduke Philip . . . found himself in a sort of
            honorable detention at Henry's court. --Hallam.
      [1913 Webster]

WordNet (r) 3.0 (2006):

detention
    n 1: a state of being confined (usually for a short time); "his
         detention was politically motivated"; "the prisoner is on
         hold"; "he is in the custody of police" [syn: detention,
         detainment, hold, custody]
    2: a punishment in which a student must stay at school after
       others have gone home; "the detention of tardy pupils"

Moby Thesaurus II by Grady Ward, 1.0:

109 Moby Thesaurus words for "detention":
   afterthought, apprehension, arrest, arrestation, arrestment, bind,
   block, blockage, blocking, bureaucratic delay, captivity, check,
   clogging, close arrest, closing up, closure, confinement,
   constriction, cramp, custody, deceleration, delay, delayage,
   delayed reaction, detainment, double take, drag, dragging, durance,
   durance vile, duress, ease-off, ease-up, fixation, flagging,
   foot-dragging, halt, hampering, hang-up, hindering, hindrance,
   holdback, holdup, house arrest, immuration, immurement, impediment,
   imprisonment, incarceration, inhibition, interference, interim,
   internment, interruption, jailing, jam, lag, lagging, let, letdown,
   letup, logjam, minus acceleration, moratorium, nab, negativism,
   nuisance value, obstruction, obstructionism, occlusion, opposition,
   paperasserie, pause, pickup, pinch, red tape, red-tapeism,
   red-tapery, repression, reprieve, resistance, respite, restraint,
   restriction, retardance, retardation, retardment, setback,
   slack-up, slackening, slow-up, slowdown, slowing, slowing down,
   slowness, slowup, squeeze, stay, stay of execution, stop, stoppage,
   stranglehold, stricture, suppression, suspension,
   term of imprisonment, tie-up, time lag, wait



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

DETENTION. The act of retaining a person or property, and preventing the
removal of such person or property.
     2. The detention may be occasioned by accidents, as, the detention of a
ship by calms, or by ice; or it may, be hostile, as the detention of persons
or ships in a foreign country, by order of the government. In general, the
detention of a ship does not change the nature of the contract, and
therefore, sailors will be entitled to their wages during the time of the
detention. 1 Bell's Com. 517, 519, 5th ed.; Mackel. Man. Sec. 210.
     3. A detention is legal when the party has a right to the property, and
has come lawfully into possession. It is illegal when the taking was
unlawful, as is the case of forcible entry and detainer, although the party
may have a right of possession; but, in some, cases, the (retention may be
lawful, although the taking may have been unlawful. 3 Penn. St. R. 20. When
the taking was legal, the detention may be illegal; as, if one borrow a
horse, to ride from A to B, and afterwards detain him from the owner, After
demand, such detention is unlawful, and the owner may either retake his
property, or have an action of replevin or detinue. 1 Chit. Pr. 135. In some
cases, the detention becomes criminal although the taking was lawful, as in
embezzlement.