congratulations (interj.)

mid-15c., from Latin congratulationem (nominative congratulatio), noun of action from past-participle stem of congratulari "wish joy," from com "together, with" (see com-) + gratulari "give thanks, show joy," from gratus "agreeable" (from suffixed form of PIE root *gwere- (2) "to favor").

1884, colloquial shortening of congratulations. Further colloquialized in British university slang to congratters (1895) and in online gamer chat shortened to grats (by 2000).