backup

• POS: Noun
• HYPHEN: back=up

CIDE DICTIONARY

backup, n. 

•  anything kept in reserve to serve as a substitute in case of failure or unavailability of the normal or primary object; -- used for devices, plans, people, etc. Also used attributively; as, there was no backup for the electrical supply; a backup motor; a backup generator.  [PJC]
•  a musician or group of musicians accompanying a soloist, whether vocalists or instrumentalists.  [PJC]
•  a person or group of persons serving as reinforcement for another or others; as, the policeman called for backup when he was fired on.  [PJC]
•  an accumulation, overflow, or reverse flow (in traffic or a liquid flow system) caused by a stoppage or other malfunction.  [PJC]
•  A copy of a program or data from a computer onto a data-storage medium, usually one that may be removed to safe storage at a distance from the computer; it is used to preserve data for use in the contingency that the original data on the computer may be lost or become unusable. A backup that is removed from the building housing the computer system (to provide protection against loss of data in a disastrous event such as a fire) is called off-site backup. Also used attributively; as, backup copy.  [PJC]
•  The act or process of creating a backup{5}; as, they performed a full system backup every weekend.  [PJC]

OXFORD DICTIONARY

backup, n.
1 moral or technical support (called for extra backup).
2 a reserve.
3 Computing (often attrib.) a the procedure for making security copies of data (backup facilities). b the copy itself (made a backup).
4 US a queue of vehicles etc., esp. in congested traffic.

Idiom

backup light US a reversing light.

THESAURUS

backup

about-face, about-turn, advocate, agent, alter ego, alternate, alternative, amicus curiae, analogy, attorney, back track, back trail, backing, backing off, backing out, backing up, backup man, champion, change, changeling, comparison, copy, counterfeit, deputy, double, dummy, equal, equivalent, ersatz, exchange, executive officer, exponent, fake, figurehead, fill-in, ghost, ghostwriter, imitation, lieutenant, locum, locum tenens, makeshift, metaphor, metonymy, mock, next best thing, paranymph, personnel, phony, pinch, pinch hitter, pleader, procurator, provisional, proxy, relief, replacement, representative, reserve, reserves, reversal, reverse, reversing, reversion, right-about, right-about-face, ringer, second in command, second string, secondary, sign, spare, spares, stand-in, stopgap, sub, substituent, substitute, substitution, succedaneum, superseder, supplanter, surrogate, swingaround, symbol, synecdoche, temporary, tentative, third string, token, turnabout, turnaround, understudy, utility, utility man, utility player, vicar, vicar general, vicarious, vice, vice-president, vice-regent, vicegerent, volte-face