Yours, Etc.: Origins and Uses of 8 Sign-Offs
early 15c., "doubling," from Middle French duplicacion (13c.) and directly from Latin duplicationem (nominative duplicatio), noun of action from past participle stem of duplicare (see duplicate (adj.)). Meaning "repetition" is from 1580s.
duplication du·pli·ca·tion (dōō'plĭ-kā'shən, dyōō'-)
The existence or growth into two corresponding parts.