on guard meaning

Adjective: on guard

1. Vigilant
   "on guard against con artists"
   - on one's guard, upon one's guard, on your guard

See also: wary

[American idiom]
cautious; watchful.
• Be on guard. There are pickpockets around here.
• You had better be on your guard.

[American slang]
adj. phr. Watchful; watching. The police warned people to he on guard for pickpockets during the Christmas rush. Two men are on guard at the door.
Antonym: OFF GUARD.

• guard:    Noun: guard & ...
• advance guard:    n. [c]a group of p ...
• advanced guard:     or advanced guard ...

Examples

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1. the man below there are always on guard.
2. and right off i was on guard against mencken's books.
3. being doubled up on guard isn't so good either.
4. against that dreadful design the church stands ever on guard.
5. he then spoke earnestly to the delaware who stood on guard.