Why is the ninth month called September?
"foresail of a ship," 1660s, gibb, of uncertain origin, perhaps related to gibbet, from notion of a sail "hanging" from a masthead [Barnhart, OED]. Or perhaps from jib (v.) "shift a sail or boom" (1690s), from Dutch gijben, apparently related to gijk "boom or spar of a sailing ship." Said to indicate a ship's character to an observant sailor as a strange vessel approaches at sea; also nautical slang for "face," hence cut of (one's) jib "personal appearance" (1821).
"agree, fit," 1813, of unknown origin, perhaps a figurative extension of earlier jib, gybe (v.) "shift a sail or boom" (see jib). OED, however, suggests a phonetic variant of chime, as if meaning "to chime in with, to be in harmony." Related: Jibed; jibes; jibing.
1560s, perhaps from Middle French giber "to handle roughly," or an alteration of gaber "to mock."
in sailing ships, triangular sail rigged to a stay extending from the foremast, or foretopmast, to the bowsprit or to a spar, the jibboom, that is an extension of the bowsprit. The jib is first known to have been used on one-masted vessels. Its use began to spread about 1600 and extended to larger war vessels about 1700. Jibs proved handy in helping to steer and were much valued-e.g., on the square-rigger, as a means of better close-hauled sailing and of setting extra sail with comparatively little labour demand. In some ships the number of jibs reached five or more, and often the jibboom itself required an extension, the flying jibboom, to carry them.