dub (v.1) Look up dub at Dictionary.com
"give a name to," originally "make a knight," from late Old English dubbian "knight by striking with a sword" (11c.), a late word, perhaps borrowed from Old French aduber "equip with arms, adorn" (11c.) of uncertain origin, but there are phonetic difficulties. Meaning "provided with a name" is from 1590s. Related: Dubbed; dubbing.
dub (v.2) Look up dub at Dictionary.com
"add or alter sound on film," 1929, shortening of double; so called because it involves re-recording voices onto a soundtrack. The type of re-mixed reggae music was so called from 1974, probably for the same reason. Related: Dubbed; dubbing.