The earliest attestation we have of the word celebrate is from a mid-fifteenth century translation of a Latin book on agriculture. At the time, it was spelled the same way (although celebrat was used in a few later instances), but it was used as a past participle meaning something more along the lines of "praised" or "esteemed". Then there was a period where it could refer to a demonstration of emotion in general, be it sadness or happiness, and by the seventeenth century it meant "celebration of joy". The word comes from Latin celebratus, which could mean "famous" or "populous" - the former sense also became our word celebrity - and that has an unknown etymology. Before the Latin term was introduced, the Old English word for "celebrate" was freolsian, which roughly translates to "free from labor".
Hello! I'm Adam Aleksic, a sophomore studying government and linguistics at Harvard University, where I co-founded the Harvard Undergraduate Linguistics Society. In addition to etymology, I also really enjoy politics, vexillology, geography, board games, conlanging, and law.