dismount

from The American Heritage® Dictionary of the English Language, 5th Edition.

• intransitive verb To get off or down, as from a horse.
• intransitive verb Sports To execute a dismount in gymnastics.
• intransitive verb To get out of a vehicle.
• intransitive verb To remove from a support, setting, or mounting.
• intransitive verb To unseat or throw off, as from a horse.
• intransitive verb To disassemble (a mechanism, for example).
• noun The act or manner of dismounting, especially from a horse.
• noun Sports A move in gymnastics whereby the gymnast gets off an apparatus or completes a floor exercise, typically landing on both feet.

from The Century Dictionary.

• To descend from a height; come or go down.
• To get off from a horse or other ridden animal; descend or alight, as a rider from the saddle: as, the officer ordered his troops to dismount.
• To throw or bring down from an elevation, or from a place or post of authority.
• To throw or bring down from a horse; unhorse: as, the soldier dismounted his adversary.
• To remove or throw down, as cannon or other artillery from their carriages, or from a parapet or intrenchment; destroy the mountings of, so as to render useless.
• To remove from a frame, setting, or other mounting: as, to dismount a picture or a jewel.

from the GNU version of the Collaborative International Dictionary of English.

• transitive verb To throw or bring down from an elevation, place of honor and authority, or the like.
• transitive verb To throw or remove from a horse; to unhorse.
• transitive verb (Mech.) To take down, or apart, as a machine.
• transitive verb To throw or remove from the carriage, or from that on which a thing is mounted; to break the carriage or wheels of, and render useless; to deprive of equipments or mountings; -- said esp. of artillery.
• intransitive verb Poetic To come down; to descend.
• intransitive verb To alight from a horse; to descend or get off, as a rider from his beast.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun gymnastics The part of a routine in which the gymnast detaches from an apparatus.
• verb transitive, intransitive to get off (something)
• verb computing, transitive to make a hard drive unavailable for use

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the act of dismounting (a horse or bike etc.)
• verb alight from (a horse)