A path of no width, and one row of written words. Also a descent of related beings, one after another.
Latin linea (a linen thread, a line drawn with one), from linum (flax); a path of no width, one row of writing, and a descent of kin all take their name from the drawn thread.
A path with no width of its own, a row of written words, and a descent of kin one after another — three things sharing a name because each is a single thread followed from one end to the other.