1. The rate
followed by anything in motion; hence, a road
or route; as, the arrow descended in a curved line; the seat
from lines of travel.
2. That which has length, but not breadth or thickness.
3. A circle of latitude or of longitude, as represented on a map. The equator; generally called the line, or equinoctial line; as, to cross the line.
4. A series or succession of ancestors or descand ants of a given face; 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. Line of force, any line in a space in which forces are acting, so drawn that at each point of the line its tangent is the direction of the resultant of all the forces. It cuts at right angles each 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.
Source: Websters Vocabulary