dub v.1

c. 1200, doublen, "to make double; increase, enlarge, or extend by adding an equal portion, measure, or value to," from Old French dobler, from Latin duplare, from duplus "twofold, twice as much" (see double (adj.)). Intransitive sense of "to become twice as great" is from late 14c.

From mid-14c. as "to duplicate;" from late 14c. as "to repeat, do twice;" from c. 1400 in the transitive sense of "lay or fold one part of upon another." By 1540s as "to pass round or by." Sense of "turn in the opposite direction" is from 1590s. Meaning "to bend or fold" (a part of the body) is from early 15c.; to double up bodily is from 1814.

A blow on the stomach "doubles up" the boxer, and occasions that gasping and crowing which sufficiently indicate the cause of the injury .... [Donald Walker, "Defensive Exercises," 1840]

Meaning "to work as, in addition to one's regular job" is c. 1920, circus slang, from performers who also played in the band. Related: Doubled; doubling.

"add (extraneous sounds) to a recording," 1954, from over- + dub (v.). As a noun (over-dub) from 1953. Related: Overdubbed; overdubbing.