4. (Science: genetics) a series or succession of ancestors or descand ants of a given person; a family or race; as, the ascending or descending line; the line of descent; the male line; a line of kings. Of his lineage am i, and his offspring By very line, as of the stock real. (Chaucer)
5. (Science: physics) line of force, any line in a space in which forces are acting, so drawn that at every point of the line its tangent is the direction of the resultant of all the forces. It cuts at right angles every equipotential surface which it meets. Specifically, the outline of a horizontal section of a vessel, as when floating in the water.
Origin: oe. Line, as. Line cable, hawser, prob. From L. Linea a linen thread, string, line, fr. Linum flax, thread, linen, cable; but the english word was influenced by f. Ligne line, from the same L. Word linea.