chair n.

1701, "pleasure carriage," from French chaise "chair" (15c.), dialectal variant of chaire (see chair (n.)) due to 15c.-16c. Parisian swapping of -r- and -s-, a habit 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," with French word order, the second word confused in English with lounge.

1580s, "church of a bishop," from phrase cathedral church (c. 1300) "principal church of a diocese," a phrase partially translating Late Latin ecclesia cathedralis "church of a bishop's seat," from a specific early Christian use of classical Latin cathedra "a teacher or professor's chair," commonly "an easy chair (principally used by ladies)," also metonymically, as in cathedrae molles "luxurious women," from Greek kathedra "chair, seat, bench," also "exalted seat occupied by men of eminent rank or influence," from kata "down" (see cata-) + hedra "seat, base, chair, face of a geometric solid" (from PIE root *sed- (1) "to sit"). The Greek word was used in Old Testament and New Testament translations.

The English word was born an adjective, and attempts to force further adjectivization onto it in 17c. yielded cathedraical (1670s), cathedratic (1660s), cathedratical (1660s), after which the effort seems to have been given up.