aider

noun

1. A person who aids or assists.

   “The capitaines of the toune seyng theire pillers borken, and their chief ayders discomfited, rendered the toune to the duke of Somerset,”

   “[…] arte is neither an aider nor a surmounter, but onely a bare immitatour of natures works, following and counterfeyting her actions and effects […]”

   “[…] being there as an assistant, he actually seemed—[…]—to be the aider and abettor of a system which filled him with honest disgust and indignation, […]”

   “The woman in question had, as she said, been a close friend of Margaret’s, and, as such, an aider in her habits of intemperance.”

2. A mountaineer's stirrup or étrier.

   “As I was switching my feet in my aiders, the hook popped.”