(s)pen- / Indo-European roots
Examples of words with the root (s)pen-: -penia, antependium, append, avoirdupois, compendium, compensate, depend, dispense, equiponderate, expend, geoponic, impend, lithopone, painter, penchant, pendant, pendentive, pendulous, pensile, pension, pensive, perpend, perpendicular, peso, poise, ponder, ponderous, pound, prepense, preponderate.
To draw, stretch, spin.
▲ Derivatives include spider, pansy, pendant1, appendix, penthouse, spontaneous.
I. Basic form *spen-.
1. Suffixed form *spen-wo-. a. spider, spin from Old English spinnan, to spin, and spīthra, spider, contracted from Germanic derivative *spin-thrōn-, "the spinner"; b. spindle from Old English spinel, spindle, from Germanic derivative *spin-ilōn-. Both a and b from Germanic *spinnan, to spin.
2. Extended form *pend-. painter2, pansy, penchant, pendant1, pendentive, pendulous, pendulum, pensile, pension1, pensive, peso, poise1; antependium, append, appendix, avoirdupois, compendium, compensate, counterpoise, depend, dispense, expend, impend, penthouse, perpend, perpendicular, prepense, propend, recompense, stipend, suspend, vilipend from Latin pendēre, to hang (intransitive), and pendere, to cause to hang, weigh, with its frequentative pēnsāre, to weigh, consider.
3. Perhaps suffixed form *pen-yā-. -penia from Greek peniā, lack, poverty (< "a strain, exhaustion").
4. geoponic, lithopone from Greek ponos, toil, and ponein, to toil, o-grade derivatives of penesthai, to toil.
II. O-grade forms *spon-, *pon-.
1. a. span2, spancel from Middle Dutch spannen, to bind; b. spanner from Old High German spannan, to stretch. Both a and b from Germanic *spannan.
2. span1 from Old English span(n), distance, from Germanic *spanno-.
3. Perhaps Germanic *spangō. spangle from Middle Dutch spange, clasp.
4. Suffixed and extended form *pond-o-. pound1 from Latin pondō, by weight.
5. Suffixed and extended form *pond-es-. ponder, ponderous; equiponderate, preponderate from Latin pondus (stem ponder-), weight, and its denominative ponderāre, to weigh, ponder.
6. Suffixed o-grade form *spon-t-. spontaneous from Latin sponte, of one's own accord, spontaneously (but this is more likely related to the Germanic verb *spanan, to entice, from a homophonous root).
[Pokorny (s)pen-(d-) 988.]