Gibbous is a word many of you will recognize in an astronomical context, as it refers to the period of time when a heavenly body is more than half, but not fully, visible to an observer. However, the adjective also has a general definition of "characterized by swelling or protuberance", which was the original meaning. The word is a Middle English borrowing from the Late Latin gibbus, meaning "hunchback", and got its modern definition because of a physical resemblance between the moon and a person hunched over. Earlier on, gibbus was a noun meaning "hump", and that, through Proto-Italic gifri, is thought to derive from Proto-Indo-European geyb, "curved". After its first attestation in Lanfranc's Science of Cirurgie, a medical book from sometime in the fifteenth century, usage of the word gibbous in literature over time peaked in the year 1750 and has been trending downward since, especially as the earlier definition is increasingly relegated to the tomes of history.
Hello! I'm Adam Aleksic, a senior studying government and linguistics at Harvard University, where I co-founded the Harvard Undergraduate Linguistics Society. In addition to etymology, I also really enjoy trivia, politics, vexillology, geography, board games, conlanging, art history, and law.