I. a-ˈfīn, ə- noun
Etymology: Anglo-French affin, from Latin affinis, from affinis related
Date: circa 1509
: a relative by marriage : in-law
II. adjective
Etymology: Latin affinis, adjective
Date: 1918
: of, relating to, or being a transformation (as a translation, a rotation, or a uniform stretching) that carries straight lines into straight lines and parallel lines into parallel lines but may alter distance between points and angles between lines
affine geometry
• af·fine·ly adverb