The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
Appendix I
Indo-European Roots
ENTRY:
skel-1
DEFINITION:
Also kel-. To cut. Derivatives include scalp, skill, cutlass, half, scalpel, and sculpture. 1a.shell, from Old English scell,sciel, shell; b.scagliola, from Italian scaglia, chip. Both a and b from Germanic *skalj, piece cut off, shell, scale. 2a.shale, from Old English sc(e)alu, husk, shell; b.scale1, from Old French escale, husk, shell. Both a and b from Germanic *skal.3a.scall, from Old Norse skalli, bald head (< “closely shaved skull”); b.scalp, from Middle English scalp, top of the head, from a source akin to Old Norse skalpr, sheath, shell. Both a and b from Germanic *skal-.4.scale3, skoal, from Old Norse skl, bowl, drinking vessel (made from a shell), from Germanic *skl.5.shield, from Old English scield, shield (< “board”), from Germanic *skelduz.6a.skill, from Old Norse skil, reason, discernment, knowledge (< “incisiveness”); b.sheldrake, from Middle English scheld, variegated, from a Low German source akin to Middle Dutch schillen, to diversify, with past participle schillede, separated, variegated. Both a and b from Germanic *skeli-.7.school2, shoal2, from Middle Low German schle, troop, or Middle Dutch scle, both from Germanic *skul, a division. 8. Suffixed variant form *kel-tro-.coulter, cultrate, cutlass, from Latin culter, knife. 9. Suffixed zero-grade form *sk-yo-.scalene, from Greek skallein, to stir up, hoe (> skalenos, uneven). 10. Extended root *skelp-.a.shelf, from Middle Low German schelf, shelf (< “split piece of wood”), from Germanic *skelf-;b. possibly Germanic *halbaz (< variant root *kelp-), divided. half, halve, from Old English healf, half; c. perhaps variant *skalp-.scalpel, sculpture, from Latin scalpere, to cut, scrape, with derivative sculpere (originally as the combining form of scalpere), to carve. (Pokorny 1. (s)kel- 923.)
, piece cut off, shell, scale. 2a. shale, from Old English sc(e)alu, husk, shell; b. scale1, from Old French escale, husk, shell. Both a and b from Germanic *skal
l, bowl, drinking vessel (made from a shell), from Germanic *sk
l
-yo-. scalene, from Greek skallein, to stir up, hoe (> skalenos, uneven). 10. Extended root *skelp-. a. shelf, from Middle Low German schelf, shelf (< “split piece of wood”), from Germanic *skelf-; b. possibly Germanic *halbaz (< variant root *kelp-), divided. half, halve, from Old English healf, half; c. perhaps variant *skalp-. scalpel, sculpture, from Latin scalpere, to cut, scrape, with derivative sculpere (originally as the combining form of scalpere), to carve. (Pokorny 1. (s)kel- 923.) 
