early 13c., from Old French aise "comfort, pleasure, well-being; opportunity," of unknown origin, despite attempts to link it to various Latin verbs.
The earliest senses in French appear to be 1. "elbow-room" (from an 11th century Hebrew-French glossary) and 2. "opportunity." This led Sophus Bugge to suggest an origin in Vulgar Latin asa, a shortened form of Latin ansa "handle," which could be used in the figurative sense of "opportunity, occasion," as well as being a possible synonym for "elbow," because Latin ansatus "furnished with handles" also was used to mean "having the arms akimbo." OED editors report this theory, and write, "This is not very satisfactory, but it does not appear that any equally plausible alternative has yet been proposed."