flunk (v.) Look up flunk at Dictionary.com
1823, American English college slang, original meaning "to back out, give up, fail," of obscure origin, traditionally said to be an alteration of British university slang funk "to be frightened, shrink from" (see funk (n.1)). Meaning "cause to fail, give a failing mark to" is from 1843. Related: Flunked; flunking.