seh₁-d-eyo-
“to keep sitting, settling”siege, sediment, sedan, sedate
Iterative of *seh₁-d- giving Latin sedēre derivs: siege, sediment, sedan, sedate, obsess.
Discussion
The form *seh₁-d-eyo- is an iterative or durative derivation from the root *sed- "to sit," extended with the *-eyo- suffix to convey the sense of continued or habitual sitting, settling, or remaining in place. Pokorny (IEW 884–887) reconstructs an extensive family under *sed-, and Rix (LIV² 513–514) specifies the root noting the nasal-infix present in some branches and the dental extension that appears in several derivatives.
The Latin reflex sedēre "to sit" generated an extraordinary family of English borrowings. Sediment is that which settles to the bottom; sedan originally denoted a covered chair in which one sat while being carried; sedate describes the composure of one who sits still. The political senses are especially revealing: president literally means "one who sits before" an assembly, from praesidēre, while session denotes a sitting of a court or legislature. Reside (to sit back, to settle in a place), subside (to sit down, to sink), and the psychologically vivid obsess (from obsidēre, "to sit upon," originally describing a besieging army) all extend the root metaphor. Greek hédra "seat, chair, base" connects to the same root with the expected loss of initial *s- in Greek.
On the Germanic side, English preserves the native inheritance with remarkable clarity: sit continues the root directly, set is its causative ("to cause to sit"), and seat is a Norse-influenced nominal form. The entire family illustrates how a culture that valued the act of settling — on land, in council, in judgment — encoded that value so deeply in its language that the metaphor of sitting still radiates through words for patience, authority, persistence, and even mental fixation.