1540s, "matter which settles by gravity to the bottom of water or other liquid," from French sédiment (16c.) and directly from Latin sedimentum "a settling, sinking down, subsidence," from stem of sedere "to settle, sit" (from PIE root *sed- (1) "to sit"). Especially in geology after 1680s.
Entries linking to sediment
Proto-Indo-European root meaning "to sit."
It forms 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 is the hypothetical source of/evidence for its existence is provided by: 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."
1760, "pertaining to or of the nature of dregs or sediment; precipitated by gravitation from a liquid;" see sediment + -ary. Sedimentary rock in geology is that formed by deposition of material previously suspended in water," attested by 1814.
Sedimental (adj.) "pertaining to dregs" is recorded from c. 1600 and might have lived long enough for a *sedimental journey pun but didn't.