Etymology
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sitting (n.)
early 13c., verbal noun from sit (v.). Meaning "a meeting of a body" is from c. 1400. Meaning "interval during which one sits" (for some purpose, especially to have one's portrait taken) is from 1706. Sitting-room first recorded 1771. Slang sitting duck "easy target" first recorded 1944; literal sense is from 1867 (it is considered not sporting to shoot at one).
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ephedra (n.)
genus of low, branchy desert shrubs, 1914, from Modern Latin (1737) from Greek ephedra, a name given by Pliny to the horsetail, literally "sitting upon," from fem. of ephedros "sitting or seated upon; sitting at or near," from epi "on" (see epi-) + hedra "seat, base, chair; face of a geometric solid," from PIE root *sed- (1) "to sit." The reason for the name is not known.
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seance (n.)

1789, "a sitting, a session," as of a learned society, originally in French contexts, from French séance "a sitting," from seoir "to sit," from Latin sedere "to sit" (from PIE root *sed- (1) "to sit"). Meaning "spiritualistic session in which intercourse is alleged to be held with ghosts of the dead" is recorded by 1845.

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sedentary (adj.)

1590s, of assemblies, parliaments, etc., "remaining in one place" (contrasted to ambulatory), from French sédentaire (16c.) and directly from Latin sedentarius "sitting, remaining in one place," from sedentem (nominative sedens), present participle of sedere "to sit; occupy an official seat, preside; sit still, remain; be fixed or settled" (from PIE root *sed- (1) "to sit").

Of occupations, etc., "requiring much sitting," by c. 1600. In reference to persons, "accustomed to long sitting," 1660s, hence "inactive, not in the habit of exercise." Related: Sedentariness.

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yeshiva (n.)
"Orthodox Jewish college or seminary," 1851, from Hebrew yesibah "academy," literally "a sitting," from yashav "to sit."
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sessile (adj.)

1725, "adhering close to the surface," from Latin sessilis "pertaining to sitting, for sitting on," from sessus, past participle of sedere "to sit" (from PIE root *sed- (1) "to sit"). In botany, of leaves, etc., "attached without any apparent projecting support," from 1753. Meaning "sedentary," of certain animals fixed to one spot, is recorded by 1860.

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sit-down (adj.)
1836 of meals, 1936 of strikes, from verbal phrase (c. 1200), from sit (v.) + down (adv.); as a noun, sit-down "act of sitting down" is from 1861.
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flagpole (n.)
also flag-pole, 1782, from flag (n.1) + pole (n.1). Flagpole-sitting as a craze is attested from 1927.
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sooterkin (n.)
1680s, imaginary rat-like after-birth believed to be gotten by Dutch women by sitting over stoves, 1680s.
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sitz-bath (n.)
1849, a hybrid, from German Sitzbad, literally "bath in a sitting position," from German sitzen (see sit (v.)) with English bath for German Bad.
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