know (one's) onions

(redirected from knows their onions)

know (one's) onions

To be very knowledgeable or skilled in some area. Primarily heard in UK, Australia. I think Nicole is our best candidate for the job—when it comes to corporate accounting, she really knows her onions.
See also: know, onion

know your onions

BRITISH, OLD-FASHIONED
If you know your onions, you know a lot about a particular subject. She really knows her onions in the historical field. Note: This may derive from the rhyming slang `onion rings', meaning `things'.
See also: know, onion

know your onions

be fully knowledgeable about something. informal
Onions is perhaps short for rhyming slang onion rings , meaning ‘things’. The phrase dates from the 1920s.
See also: know, onion
References in periodicals archive ?
You're about to find out which of the nation's celebs truly knows their onions - and which have curried no favour with the nation's two pickiest gastronomes.
And, I can tell you, with little fear of contradiction from anybody who knows their onions, that the French, on the whole, cook with far greater skill and finesse than the Spaniards.
Anyone who knows their onions recognise them as one of the first root crops to be cultivated by man with a history starting in Asia and going back more than 5,000 years.