"small, hanging piece from a garment," c. 1400, of uncertain origin but probably from a Scandinavian source (compare Norwegian tagg "point, prong, barb," Swedish tagg "prickle, thorn") and related to Middle Low German tagge "branch, twig, spike"), from Proto-Germanic *tag-. The sense development might be "point of metal at the end of a cord, string, etc.," hence "part hanging loose." Or perhaps ultimately from PIE *dek-, a root forming words referring to "fringe; horsetail; locks of hair" (see tail (n.1)).
Meaning "a label" is first recorded 1835; sense of "automobile license-plate" is recorded from 1935, originally underworld slang. Meaning "an epithet, popular designation" is recorded from 1961, hence slang verb meaning "write graffiti in public places" (1990).
"to furnish with a tag," late 14c. (implied in tagged), from tag (n.1). Meaning "go along as a follower" is from 1670s; sense of "follow closely and persistently" is from 1884. Related: Tagging. Verbal phrase tag along is first recorded 1900.
"a touch in the game of tag," 1878; in baseball, 1904, from tag (n.2); the adjective in the pro-wrestling sense is recorded from 1955. Related: Tagged; tagging.