"a seat with a back, intended for one person," early 13c., chaere, from Old French chaiere "chair, seat, throne" (12c.; Modern French chaire "pulpit, throne;" the more modest sense having gone since 16c. with variant form chaise), from Latin cathedra "seat" (see cathedral).
Figurative sense of "seat of office or authority" c. 1300 originally was of bishops and professors. Meaning "office of a professor" (1816) is extended from the seat from which a professor lectures (mid-15c.). Meaning "seat of a person presiding at meeting" is from 1640s. As short for electric chair from 1900. Chair-rail "strip or board of wood fastened to a wall at such a height as to prevent the plaster from being scraped by the backs of chairs" is from 1822.
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.