to put one on his guard
Preserved but no longer current.
Meaning · English
To "give him the tip," show him where the danger lies. A guardroom is the place where military offenders are detained; and a guardship is a ship stationed in a port or harbour for its defence.
Era: ca. 1898 (Victorian)
Sources & notes
Reproduced from Brewer’s Dictionary of Phrase and Fable (1898 edition, public domain; archive.org, retrieved 2026-07-31; OCR text, minor errors possible). Reflects the scholarship and attitudes of its era.
Common questions
What does “to put one on his guard” mean?
To "give him the tip," show him where the danger lies. A guardroom is the place where military offenders are detained; and a guardship is a ship stationed in a port or harbour for its defence.
Is “to put one on his guard” formal or informal?
No register label has been reviewed yet — treat it as neutral and check the usage notes above.