1701, "pleasure carriage," from French chaise "chair" (15c.), dialectal variant of chaire (see chair (n.)) due to 15c.-16c. Parisian accent swapping of -r- and -s-, a habit often satirized by French writers. French chair and chaise then took respectively the senses of "high seat, throne, pulpit" and "chair, seat," but this was after chair had been borrowed into English in the older sense.
Originally a one-horse, two-wheeled carriage for two persons, later extended to other types of pleasure or travelling carriages. Chaise lounge (1800) is corruption of French chaise longue "long chair," the second word confused in English with lounge.