The French expression “en connaître un rayon” translates literally to “to know a department [in a store]”. English meanings include:
- to be really clued in
- to know your stuff
- to know a thing or two
French-to-French meaning is “etre calé” (to be good at something) and “savoir beaucoup” (to know a a lot).
Here’s an example sentence:
Il habite dans ces montagnes depuis plus que vingt ans. Il connaît toutes les pistes de randonees comme sa poche. En fait, on peut dire qu’il en connaît un rayon. He’s lived in these mountains for more than 20 years. He knows all the hiking trails like the back of his hand. Actually, you can say he knows his stuff.
A synonym is “s’y connaître en + subject”:
- Il s’y connait en français. He knows a thing or two about French.