WordNet (r) 3.0 (2006):

imprisonment
    n 1: putting someone in prison or in jail as lawful punishment
    2: the state of being imprisoned; "he was held in captivity
       until he died"; "the imprisonment of captured soldiers"; "his
       ignominious incarceration in the local jail"; "he practiced
       the immurement of his enemies in the castle dungeon" [syn:
       captivity, imprisonment, incarceration, immurement]
    3: the act of confining someone in a prison (or as if in a
       prison) [syn: imprisonment, internment]

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "imprisonment":
   beleaguerment, besetment, blockade, blockading, captivity,
   circumscription, close arrest, confinement, cordoning, custody,
   detention, dismemberment, durance, durance vile, duress, enclosure,
   envelopment, estrapade, galleys, hard labor, house arrest,
   immuration, immurement, impalement, incarceration, inclusion,
   internment, jailing, keelhauling, martyrdom, penal servitude,
   picketing, quarantine, railriding, remand, rock pile, siege,
   strappado, tar-and-feathering, term of imprisonment, the gantlet,
   torment, torture



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

IMPRISONMENT. The restraint of a person contrary to his will. 2 Inst. 589;
Baldw. Rep. 239, 600. Imprisonment is either lawful or unlawful; lawful
imprisonment is used either for crimes or for the appearance of a party in a
civil suit, or on arrest in execution.
     2. Imprisonment for crimes is either for the appearance of a person
accused, as when he cannot give bail; or it is the effect of a sentence, and
then it is a part of the punishment.
     3. Imprisonment in civil cases takes place when a defendant on being
sued on bailable process refuses or cannot give the bail legally demanded,
or is under a capias ad satisfaciendum, when he is taken in execution under
a judgment. An unlawful imprisonment, commonly called false imprisonment,
(q.v.) means any illegal imprisonment whatever, either with or without
process, or under color of process wholly illegal, without regard to any
question whether any crime has been committed or a debt due.
     4. As to what will amount to an imprisonment, the most obvious modes
are confinement in a prison or a private house, but a forcible detention in
the street, or the touching of a person by a peace officer by way of arrest,
are also imprisonments. Bac. Ab. Trespass, D 3; 1 Esp. R. 431, 526. It has
been decided that lifting up a person in his chair, and carrying him out of
the room in which he was sitting with others, and excluding him from the
room, was not an imprisonment; 1 Chit. Pr. 48; and the merely giving charge
of a person to a peace officer, not followed by any actual apprehension of
the person, does not amount to an imprisonment, though the party to avoid
it, next day attend at a police; 1 Esp. R. 431; New Rep. 211; 1 Carr. &
Payn. 153; S. C. II Eng. Com. Law, R. 351; and if, in consequence of a
message from a sheriff's officer holding a writ, the defendant execute and
send him a bail bond, such submission to the process will not constitute an
arrest. 6 Barn. & Cress. 528; S. C. 13 Eng. Com. Law Rep. 245; Dowl. & R.
233.
Vide, generally, 14 Vin. Ab. 342; 4 Com. Dig. 618; 1 Chit. Pr. 47; Merl.
Repert. mot Emprisonment; 17 Eng. Com. L. R. 246, n.