The Collaborative International Dictionary of English v.0.48:

Arranger \Ar*ran"ger\, n.
   One who arranges. --Burke.
   [1913 Webster]

WordNet (r) 3.0 (2006):

arranger
    n 1: a person who brings order and organization to an
         enterprise; "she was the organizer of the meeting" [syn:
         organizer, organiser, arranger]
    2: a musician who adapts a composition for particular voices or
       instruments or for another style of performance [syn:
       arranger, adapter, transcriber]