Idiom
know one's onions
Meanings
To be knowledgeable and skilled in a particular area; to be competent and well-informed.
Definition
To know one's onions means to be very knowledgeable and competent about a particular subject or job.
If you know your onions, you understand a topic or task well and can do it competently. It is often used to praise someone’s expertise or reliability at work. The phrase is common in British English and is usually informal.
Examples
- Ask Priya about mortgages—she really knows her onions.
- Our new mechanic knows his onions, so the car was fixed in minutes.
- If you know your onions, you’ll spot the mistake straight away.
- He talks confidently, but I’m not sure he knows his onions.
- She knows her onions when it comes to negotiating contracts.
Common mistake
Learners sometimes use this idiom to mean “know someone well,” but it means being skilled or knowledgeable about a subject.
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More idioms
- Bob's your uncle Used to say that something will be easy or will happen exactly as expected after a simple step.
- close but no cigar Used to say someone almost succeeded but did not quite achieve the goal.
- down to the wire Used to say something is decided or finished only at the last possible moment.
- lost the plot To become confused or behave in a way that no longer makes sense.
- ducks in a row To have everything organized and ready for action.