In reply to Old Mountain Git:
> I'm still trying to figure out when trousers became pants. What do we wear under pants?
One wears underpants under pants, obviously!
"Pants" is (I think) older, from "pantaloon". For some reason, the word "trousers" (from Scots/Irish "trews", "trous") then took over.
Then, since the word "pants" was not being used, "underpants" got shortened to "pants".
So "pants" for trousers is a reversion to an older usage.
Post edited at 14:03