"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.
Meaning "true, direct, honest" is from 1520s. Of communication, "clear, unambiguous," from 1862. Sense of "undiluted, uncompromising" (as in straight whiskey, 1874) is American English, first recorded 1856. As an adverb from c. 1300, "in a straight line, without swerving or deviating." Theatrical sense of "serious" (as opposed to popular or comic) is attested from 1895; vaudeville slang straight man first attested 1923.
Go straight in the underworld slang sense is from 1919; straighten up "become respectable" is from 1907. To play it straight is from 1906 in theater, 1907 in sports ("play fair"), with figurative extension; later perhaps also from jazz. Straight arrow "decent, conventional person" is 1969, from archetypal Native American brave name. Straight shooter is from 1928. Straight As "top grades" is from 1920.