The presiding officer of a meeting or committee, or the administrative officer of a department of instruction (as in a college). And finally, a carrier of a sedan chair.
The origin is, as you might guess, a compound of the words ‘chair’ and ‘man.’ The ‘chair’ is a reference to a seat or position of authority and the ‘man’ is, of course, a reference to the person who occupies it. The word is first found in print in 1654 when it appears in John Trapp’s Commentary of the Book of Job. So it was probably in spoken use for a few years before that.
In the 1650s, the word meant “occupier of a chair of authority.” In 1730, it meant “member of a corporate body chosen to preside at meetings.” “Chairwoman” in this sense was first attested in 1752; “chairperson” in 1971.
In the last thirty years or so, the word has been criticized for being sexist, since not all such leaders are male. The traditionalists who wanted to preserve the old patterns of speech hit back with a false etymology that states the -man is not a reference to a person at all and is, therefore, not sexist. This false etymology states that the -man comes from the Latin manus, meaning “hand,” that the chairman is the hand of the one sitting in the chair guiding the meeting. That salvo did not, and cannot, work, because it isn’t true.
The shorter form “chair” also dates back to the 17th century, meaning the person in charge of a meeting. “Chair” in this sense had another meaning. In the 1600s and subsequently, the noun “chair” was used as symbolic shorthand (a process known as “metonymy”) for the person who sat in the chair of power, much as “the Crown” is used to refer to the King or Queen or “the White House” is used to mean the current presidential administration. While this use of “chair” became common in the internal workings of organizations in the 1970s, “chair” became newly popular in general usage as a way to avoid using the gender-specific “chairman” without resorting to the stilted “chairperson” (which also appeared in the 1970s).
I don’t think I’ll ever be able to look at a chairman of the board again without visualizing him or her carrying a sedan chair.