1680s, of objects, "to sink to the bottom," from Latin subsidere "sit down, settle, sink, fall; remain; crouch down, squat," from sub "under, beneath" (see sub-) + sidere "to settle," related to sedere "to sit" (from PIE root *sed- (1) "to sit").

In reference to feelings, excitement, etc., "cease from action, become less violent or agitated, become calm or tranquil," c. 1700. By 1721 of winds. Of liquid surfaces, "to sink to a lower level, be reduced" from 1706. Related: Subsided; subsiding.

"held in reserve, held ready to furnish assistance," 1540s, from Latin subsidiarius "belonging to a reserve, of a reserve, reserved; serving to assist or supplement," from subsidium "a help, aid, relief, troops in reserve" (see subsidy).

As a noun, c. 1600, "subsidiary thing, one who or that which contributes aid or additional support." The Latin adjective also was used in Latin as a noun meaning "the reserve."

1755, "secure the services of (mercenaries, foreign troops, etc.) by payment of a subsidy," from subsidy + -ize. Also of nations, "to buy neutrality or alliance."

A sense of "secure the services of by bribery" is from 1815. The meaning "support by grants of (often government) money" is from 1828. Related: Subsidized; subsidizing.

Proto-Indo-European root meaning "to sit."

It might form all or part of: assess; assiduous; assiento; assize; banshee; beset; cathedra; cathedral; chair; cosset; dissident; dodecahedron; Eisteddfod; ephedra; ephedrine; ersatz; icosahedron; inset; insidious; nest; niche; nick (n.) "notch, groove, slit;" nidicolous; nidification; nidus; obsess; octahedron; piezo-; piezoelectric; polyhedron; possess; preside; reside; saddle; sanhedrim; seance; seat; sedan; sedate; (adj.) "calm, quiet;" sedative; sedentary; sederunt; sediment; see (n.) "throne of a bishop, archbishop, or pope;" sessile; session; set (v.); sett; settle (n.); settle (v.); siege; sit; sitz-bath; sitzkrieg; size; soil (n.1) "earth, dirt;" Somerset; soot; subside; subsidy; supersede; surcease; tanist; tetrahedron; Upanishad.

It might also be the source of: Sanskrit a-sadat "sat down," sidati "sits," nidah "resting place, nest;" Old Persian hadis "abode;" Greek ezesthai "to sit," hedra "seat, chair, face of a geometric solid;" Latin sedere "to sit; occupy an official seat, preside; sit still, remain; be fixed or settled," nidus "nest;" Old Irish suide "seat, sitting," net "nest;" Welsh sedd "seat," eistedd "sitting," nyth "nest;" Old Church Slavonic sežda, sedeti "to sit," sedlo "saddle," gnezdo "nest;" Lithuanian sėdėti "to sit;" Russian sad "garden," Lithuanian sodinti "to plant;" Gothic sitan, Old English sittan "to sit."