The Collaborative International Dictionary of English v.0.48:

Amanuensis \A*man`u*en"sis\, n.; pl. Amanuenses. [L., fr. a,
   ab + manus hand.]
   A person whose employment is to write what another dictates,
   or to copy what another has written.
   [1913 Webster]

WordNet (r) 3.0 (2006):

amanuensis
    n 1: someone skilled in the transcription of speech (especially
         dictation) [syn: stenographer, amanuensis, shorthand
         typist]