know (one's) onions

(redirected from know his 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—she really knows her onions about corporate accounting.
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