Sentence:  ... 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 <WSD>abettor</WSD> of a system which filled him with honest disgust and indignation, he loathed himself ... 
Meaning of the word marked with <WSD> tags:  A supporter or advocate. (Late 16th century.)<ref name=SOED/>