Chapter Central Sun to Chair of C by Brewer's Phrase & Fable

The word is also applied to the office of a professor, etc., as “The chair of poetry, in Oxford, is now vacant.” The word is furthermore applied to the president of a committee or public meeting. Hence-
   To take the chair. To become the chairman or president of a public meeting. The chairman is placed in a chair at the head of the table, or in some conspicuous place like the Speaker of the House of Commons, and his decision is absolutely final in all points of doubt. Usually the persons present nominate and elect their own chairman; but in some cases there is an ex officio chairman.

Chair When members of the House of Commons and other debaters call out “Chair,” they mean that the chairman is not properly supported, and his words not obeyed as they ought to be. Another form of the same expression is, “Pray support the chair.”
   Groaning chair. The chair in which a woman is confined or sits afterwards to receive congratulations. Similarly “groaning cake” and “groaning cheese” are the cake and cheese which used to be provided in “Goose month.”

“For a nurse, the child to dandle,
Sugar, soap, spiced pots, and candle
A groaning chair, and eke a cradle”
Poor Robin's Almanack, 1676.