One line saying what a thing is for. A tagline is the shortest honest form of a promise.
A compound of tag (Middle English tagge, a small attached piece) and line, Latin linea (a linen thread, a drawn line); one short line meant to be attached to a thing and carried with it wherever it goes.
One line saying what a thing is for. The shortest honest form a promise can take, made to travel attached to whatever it describes.