"knickers" - it's an abbreviation from "knickerbockers", which I gather got its meaning of baggy pants from the illustrations by Cruickshank to a book by Washington Irving back in 1848, which had as its pretended author a Dutch New Yorker, Diedrich Knickerbocker. The word has settled in England as the normal word for underpants, but I believe it isn't used much in the States where it came from.

I hope that's enough etymology to be going on with...