Yes, hat. Not that there’s any surprise in the fact that hat itself has been in the English language since the dawn of the English language. But I was interested in some of the idioms containing it. =)
Specifically, today I said something about our right as women to change our opinions at “the drop of a hat.” I pretty much knew where the saying came from–dropping a hat as a signal for a race or a fight–but I didn’t know when it came about. As it turns out, the first written reference the site I was on could find was from 1837, but it was already being used metaphorically in that context, so one can be certain it had been around for a while already.
“To eat one’s hat”–what one will do if the unlikely happens–dates from 1770. “To throw one’s hat in the ring” is from 1847, and “hat trick”–3 goals in one game–was originally of cricket in 1879 but was extended to other sports, especially hockey, by 1909. This usage actually comes from literal tricks (sleight of hand/magic tricks) involving hats in the late 1800s, but pulling off the feat supposedly used to entitle the player to a hat from his club too.