sed- / Indo-European roots
Examples of words with the root sed-: -hedron, assess, assiduous, banshee, beset, cathedra, cosset, dissident, edaphic, eisteddfod, ephedra, ersatz, exedra, eyas, insidious, isopiestic, nest, niche, nide, nidicolous, nidifugous, nidify, nidus, obsess, piezo-, possess, preside, reside, saddle, Sanhedrin.
▲ Derivatives include sit, soot, séance, siege, obsess, subside, soil1, chair.
I. Basic form *sed-.
1. Suffixed form *sed-yo-. a. sit from Old English sittan, to sit; b. sitz bath, sitzmark from Old High German sizzen, to sit. Both a and b from Germanic *sitjan.
2. Suffixed form *sed-lo-, seat. settle from Old English setl, seat, from Germanic *setlaz.
3. Suffixed (stative) form *sed-ē-. séance, sedentary, sederunt, sedile, sediment, sessile, session, sewer2, siege; assess, assiduous, assize, dissident, insidious, obsess, possess, preside, reside, subsidy, supersede, surcease from Latin sedēre, to sit.
4. Suffixed form *sed-rā-. -hedron; cathedra, cathedral, chair, ephedrine, exedra, Sanhedrin from Greek hedrā, seat, chair, face of a geometric solid.
5. Prefixed and suffixed form *pi-sed-yo-, to sit upon (*pi, on; see epi) piezo-; isopiestic from Greek piezein, to press tight.
6. Basic form *sed-. a. edaphic from Greek edaphos, ground, foundation (with Greek suffix -aphos); b. Upanishad from Sanskrit upaniṣad, Upanishad, from -sad, sitting; c. tanist from Old Irish tánaise, designated successor, from Celtic *tānihessio-, "one who is waited for" from *to-ad-ni-sed-tio, from *to-ad-ni-sed-, to wait for (*ad-, to; see ad-).
II. O-grade form *sod-.
1. Perhaps suffixed form *sod-dhlo-. saddle from Old English sadol, saddle, from Germanic *sadulaz, seat, saddle.
2. Suffixed (causative) form *sod-eyo-. a. set1 from Old English settan, to place; b. beset from Old English besettan, to set near; c. ersatz from Old High German irsezzan, to replace, from sezzan, to set. a-c all from Germanic *(bi-)satjan, to cause to sit, set.
3. Suffixed form *sod-yo-. soil1 from Latin solium, throne, seat.
III. Zero-grade form *-sd- (in compounds), assimilated to *-zd-.
1. Reduplicated form *si-sd- becoming *si-zd-. a. subside from Latin sīdere, to sit down, settle; b. synizesis from Greek hizein, to sit down, settle down.
2. Compound suffixed form *ni-zd-o-, nest, literally "(bird's place of) sitting down" (*ni-, down). a. nest from Old English nest, from Germanic *nistaz; b. niche, nick, nide, nidus; eyas, nidicolous, nidifugous, nidify from Latin nīdus. nest.
3. Compound suffixed form *kuzdho-zd- (see (s)keu-)
IV. Lengthened-grade form *sēd-.
1. see2 from Latin sēdēs, seat, residence.
2. Suffixed form *sēd-i-, settler. cosset possibly from Old English -sǣta, -sǣte, inhabitant(s), from Germanic *sētōn-, *sēti-.
3. Suffixed form *sēd-yo-. seat from Old Norse sæti, seat, from Germanic *(ge)sētjam, seat (*ge-,*ga-, collective prefix; see kom)
4. Suffixed form *sēd-ā-. sedate1 from Latin sēdāre, to settle, calm down.
5. Suffixed form *sēd-es-, seat. banshee from Old Irish síd, fairy mound.
V. Lengthened o-grade form *sōd-. soot from Old English sōt, soot (< "that which settles"), from Germanic *sōtam, from suffixed form *sōd-o-.
[Pokorny sed- 884.]