keelson (n.)

also kelson, "line of jointed timbers in a ship laid on the middle of the floor-timbers over the keel, binding the floor-timbers to the keel," 1620s, altered (by influence of keel (n.)) from Middle English kelsyng (late 13c.), which probably is of Scandinavian origin (compare Swedish kölsvin, Danish and Norwegian kjølsvin), from a compound of words such as Old Norse kjölr (see keel (n.)) + swin "swine," which was used of timber (see swine), or perhaps the second element is a folk-etymology alteration of another word (such as Norwegian svill "sill"). Or else the whole is from a similarly formed Low German source (kielschwin).