know one's onionsとは 意味・読み方・使い方

動詞

know one's onions (三人称単数 現在形 knows one's onions, 現在分詞 knowing one's onions, 過去形 knew one's onions, 過去分詞 known one's onions)

1. (informal) Synonym of know one's stuff, to be knowledgeable about a given subject or task.
   • 2007 February 20, Chris Chibnall, Life on Mars, Season 2, Episode 2:

     Sam Tyler: Well, our first priority is to make sure the thieves don't strike again. It'll be tricky, 'cause these sorts of gangs rarely have just one target on the go. They've usually researched half a dozen possibilities, waiting for the most opportune circumstances on any of them.
     Harry Woolf: He knows his onions, this lad, eh?
     Gene Hunt: Oh, he's a right little smart-arse. So, what do you suggest, Buddha?

   Joe really knows his onions when it comes to cooking.

参照

• “know one's onions”, in Collins English Dictionary.