break a leg 1
Fracture one or more leg bones, as in She fell down the stairs and broke her leg in two places. [c. a.d. 1000]
Good luck! as in Play well, Rob—break a leg! The origin of this imperative to a performer about to go onstage is unclear; it may have been a translation of the German Hals und Beinbruch (“Break your neck and leg”), also of unknown origin. Equally mysterious is the Italian equivalent, In bocca di lupe, “Into the mouth of the wolf.” [c. 1900]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.