Amanuensis

According to Merriam Webster:

Main Entry: aman·u·en·sisPronunciation: \ə-ˌman-yə-ˈwen(t)-səs\

Function: noun

Inflected Form(s): plural aman·u·en·ses \-(ˌ)sēz\

Etymology: Latin, from (servus) a manu slave with secretarial duties

Date: 1619

: one employed to write from dictation or to copy manuscript

Context: Mastered by Love, by Stephanie Laurens. 

Example sentence: I refuse to work as an amanuensis. In fact, if you want me to me your amanuensis, I'm going to have to insist that you talk to this hand.