on (one's) guard
- idiom
- You need to be on your guard when dealing with unfamiliar websites.
Examples
-
...it's best to be on one's guard.
-
After hearing about recent thefts, I stayed on my guard while walking home at night.
-
The lifeguard remained on guard to ensure the safety of everyone at the pool.
Synonyms
206
2.9
Careful to avoid risk or mistakes
102
3.6
Careful because you do not trust someone or something
71
6.0
A person who keeps careful watch for danger or problems
45
3.5
Alert and ready to act if danger or problems appear
36
3.2
Being careful and ready to notice danger or problems
15
5.2
Aware of possible danger or change
5
4.4
Ready and alert to notice danger or problems
2
8.6
Very alert and watchful because of fear or past harm
1
4.7
Alert and ready to deal with danger or problems
You are ready and alert to act quickly
Antonyms
How Alert
Surface Forms
Morphology
on + (one's) + guard
The meaning 'alert and ready' is directly inferable from 'on' (indicating state/position) plus 'guard' (protection/vigilance), so a learner who knows the constituents can compose the sense. The possessive '(one's)' is a slot filler and the construction has clear parallels in many languages (e.g. Spanish 'estar en guardia', French 'être sur ses gardes'), supporting immediate comprehensibility.
Etymology
The idiom on your guard comes from the image of a guard standing watch and looking for danger. So, when you are on your guard, you are 'alert and ready'.