Words related to *sed-
1610s, "shallow recess in a wall," from French niche "recess (for a dog), kennel" (14c.), perhaps from Italian nicchia "niche, nook," which is said to be from nicchio "seashell," itself said by Klein, Barnhart, etc. to be probably from Latin mitulus "mussel," but the change of -m- to -n- is not explained (Century Dictionary compares napkin from Latin mappa). Watkins suggests that the word is from an Old French noun derived from nichier "to nestle, nest, build a nest," via Gallo-Roman *nidicare from Latin nidus "nest" (see nidus), but that, too, has difficulties. The figurative sense is recorded by 1725. Biological use dates from 1927.
"notch, groove, slit," mid-15c., nik, nyke, a word of unknown origin, possibly from a variant of Old French niche (see niche). Nick of time is first attested 1640s (nick of opportunity is 1610s), possibly from an old custom of recording time as it passed by making notches on a tally stick, though nick in the general sense of "critical moment" is older (1570s, Hanmer, who adds "as commonly we say") than the phrase. Nick (n.) specifically as "notch of a tally" is attested from late 15c.
of birds, "bearing young which are helpless at birth," 1896, from Modern Latin Nidicolae (1894), the zoologists' collective name for the species of birds having the young born in a more or less helpless condition, unable to leave the nest for some time and fed directly by the parent, from Latin nidus "nest" (see nest (n.)) + colere "to inhabit" (see colony). Contrasted to nidifugous birds (1902), whose young are well-developed and leave the nest at birth (from Latin fugere "to flee").
c. 1500, "to besiege" (a sense now obsolete), from Latin obsessus, past participle of obsidere "watch closely; besiege, occupy; stay, remain, abide" literally "sit opposite to," from ob "against" (see ob-) + sedere "to sit," from PIE root *sed- (1) "to sit." Of evil spirits, "to haunt," from 1530s. The psychological senseof "to haunt as a fixed idea" developed gradually from 1880s and emerged 20c. The 1895 Century Dictionary has only the two senses "to besiege" (marked obsolete) and "to attack, vex, or plague from without." Related: Obsessed; obsessing.
word-forming element meaning "pressure," from Greek piezein "to press tight, squeeze," from PIE *pisedyo- "to sit upon" (source also of Sanskrit pidayati "presses, oppresses"), from *pi "on," short for *epi (see epi-) + root *sed- (1) "to sit." First in piezometer (1820), an instrument for ascertaining or testing pressure. It was in common use in word formation from c. 1900.
"a solid bounded by many (usually more than 6) plane faces," 1560s, from Latinized form of Greek polyedron, neuter of adjective polyedros "having many bases or sides," from polys "many" (from PIE root *pele- (1) "to fill") + hedra "seat, base, chair, face of a geometric solid" (from PIE root *sed- (1) "to sit").