Yours, Etc.: Origins and Uses of 8 Sign-Offs
1857, racing slang, "to refuse or avoid payment of money laid as a bet," probably a disparaging use of the national name Welsh. Related: Welched; welching.
Welch (wělch, wělsh), William Henry. 1850-1934. American pathologist and bacteriologist who discovered the bacteria that causes gas gangrene.