abettor

noun

Etymology: From Middle English abettour, from Anglo-Norman abettour, from Old French abeter + -our (“-or”). See abet.

1. One that abets an offender; one that incites; instigates; encourages.

   “Thou foul abettor! thou notorious bawd! Thou plantest scandal and displacest laud:”

2. A supporter or advocate.

   “[…] when he recollected that, being there as an assistant, he actually seemed—no matter what unhappy train of circumstances had brought him to that pass—to be the aider and abettor of a system which filled him with honest disgust and indignation, he loathed himself […]”