Gibbously is an adjective that means "bulging or protruding." Some synonyms for gibbously include: swelling, bloated, distended, protruding, curving outward, convex, and rounded. These words all evoke the idea of something that is round, plump, swollen, or bulging. Some antonyms for gibbously might include: concave, sunken, depressed, or flat. These words help convey the opposite meaning of gibbously. The choice of synonym will depend on the context in which the word is being used and the tone or mood the writer is trying to convey.