verb (used with object)

verb (used without object)

to take precautions (usually followed by against): to guard against errors.
to give protection; keep watch; be watchful.



    off guard, unprepared; unwary: The blow from behind caught him off guard.Also off one's guard.
    on guard, vigilant; wary: on guard against dishonest merchants.Also on one's guard.
    stand guard over, to watch over; protect: The dog stood guard over his wounded master.

Origin of guard

1375–1425; late Middle English garde guardianship < Old French g(u)arde, noun derivative of g(u)arder (v.) < Germanic; see ward
Related formsguard·a·ble, adjectiveguard·er, nounguard·less, adjectiveguard·like, adjectivepre·guard, verb (used with object)self-guard, nounun·der·guard, nounun·guard·a·ble, adjective

Synonyms for guard

Synonym study

1. See defend.

Antonyms for guard

1. attack. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Related Words for on one's guard

alert, careful, cautious, defensive, guarded, heedful, mindful, observant, vigilant, watchful

British Dictionary definitions for on one's guard



to watch over or shield (a person or thing) from danger or harm; protect
to keep watch over (a prisoner or other potentially dangerous person or thing), as to prevent escape
(tr) to controlto guard one's tongue
(intr usually foll by against) to take precautions
to control entrance and exit through (a gate, door, etc)
(tr) to provide (machinery, etc) with a device to protect the operator
  1. chess cardsto protect or cover (a chess man or card) with another
  2. curling bowlsto protect or cover (a stone or bowl) by placing one's own stone or bowl between it and another player
(tr) archaic to accompany as a guard


a person or group who keeps a protecting, supervising, or restraining watch or control over people, such as prisoners, things, etcRelated adjective: custodial
a person or group of people, such as soldiers, who form a ceremonial escortguard of honour
British the official in charge of a train
  1. the act or duty of protecting, restraining, or supervising
  2. (as modifier)guard duty
Irish another word for garda
a device, part, or attachment on an object, such as a weapon or machine tool, designed to protect the user against injury, as on the hilt of a sword or the trigger of a firearm
anything that provides or is intended to provide protectiona guard against infection
  1. another name for safety chain
  2. a long neck chain often holding a chatelaine
sport an article of light tough material worn to protect any of various parts of the body
  1. the position of the two players in a team who play furthest from the basket
  2. a player in this position
the posture of defence or readiness in fencing, boxing, cricket, etc
take guard cricket (of a batsman) to choose a position in front of the wicket to receive the bowling, esp by requesting the umpire to indicate his position relative to the stumps
give guard cricket (of an umpire) to indicate such a position to a batsman
off one's guard having one's defences down; unprepared
on one's guard prepared to face danger, difficulties, etc
stand guard (of a military sentry, etc) to keep watch
mount guard
  1. (of a sentry) to begin to keep watch
  2. (with over)to take up a protective or defensive stance (over something)
Derived Formsguardable, adjectiveguarder, nounguardless, adjectiveguardlike, adjective

Word Origin for guard

C15: from Old French garde, from garder to protect, of Germanic origin; compare Spanish guardar; see ward
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for on one's guard



early 15c., "one who keeps watch," from Middle French garde "guardian, warden, keeper; watching, keeping, custody," from Old French garder "to keep, maintain, preserve, protect" (corresponding to Old North French warder, see gu-), from Frankish *wardon, from Proto-Germanic *wardo- "to guard" (see ward (v.)). Abstract or collective sense of "a keeping, a custody" (as in bodyguard) also is from early 15c. Sword-play and fisticuffs sense is from 1590s. Guard-rail attested from 1860.



mid-15c., from guard (n.) or from Old French garder "to keep watch over, guard, protect." Related: Guarded; guarding.

Online Etymology Dictionary, © 2010 Douglas Harper

Idioms and Phrases with on one's guard

on one's guard

see under off guard.


see off guard; stand guard.

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.