- any of various fore-and-aft structural members lying above or parallel to the keel in the bottom of a hull.
- a longitudinal beam fastened to the keel of a vessel for strength and stiffness
also kelson, 1620s, altered (by influence of keel (n.)) from Middle English kelsyng (late 13c.), which probably is of Scandinavian origin (cf. Swedish kölsvin, Danish and Norwegian kjølsvin, from root of Old Norse kjölr (see keel (n.)) + swin “swine,” used of timber (see swine). Or else from a similar Low German source.