make (one’s) bones
v.— «They have reinstituted the requirement that before someone is made a soldier, he will have to ‘make his bones.’ That is, he will have to kill someone.» —“FBI Agent Nearly Was Inducted Into Mafia” by Larry Margasak AP Apr. 22, 1988. (source: Double-Tongued Dictionary)
Further reading
Cat hair may be something you brush off, but cat hair is also a slang term that means “money.” In the same way, cat beer isn’t alcoholic — some people use cat beer as a joking term for “milk.” And imagine walking on a...
There are eight major planets, but more than a million minor ones, including asteroids. If you discover one, you get the honor of naming it. The Dictionary of Minor Planet Names includes minor planets named for rock bands, jazz musicians, poets, and...