Couteau

Ils sont à couteaux tirés = They are at daggers drawn.

[Formerly: Ils en sont aux couteaux tirés.]

Aller en Flandre sans couteau = To embark in an enterprise without the necessary resources.

[Also: Aller aux mûres sans crochet.]

C'est comme le couteau de Jeannot = That is like the Irishman's gun (said of anything that has been mended so often as to have nothing of the original left).