en pas|sant

en pas|sant «ahn pah sahn», French.

1. in passing; by the way; incidentally: »

If I could drop a word en passant into the Sultan's ear, the syndicate would be overjoyed to set aside a few shares of stock for both of us (New Yorker).

2. a form of pawn capture in chess. If a pawn in its first move passes over a square controlled by an opposing pawn, the opposing pawn has the right to capture it immediately while advancing to that square. »

Why, you're so rusty you've forgotten the rules about castling and pawn taking pawn en passant (Punch).