The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
Appendix I
Indo-European Roots
ENTRY:
gleubh-
DEFINITION:
To tear apart, cleave. Derivatives include clever and hieroglyphic. I. Basic form *gleubh-.1.cleave1, from Old English clofan, to split, cleave, from Germanic *kleuban.2. Probably o-grade form *gloubh-.clever, from Middle English cliver, nimble, skillful, perhaps akin to East Frisian klüfer,klifer, skillful, and Old Norse kleyfr, easy to split, from Germanic *klaubri-. II. Zero-grade form *glubh-.1a.clove2, from Old English clufu, clove (of garlic); b.kloof, from Middle Dutch clove, a cleft; c.clevis, from a Scandinavian source akin to Old Norse klofi, a cleft. a–c all from Germanic *klub-, a splitting. 2.cleft, from Old English geclyft, fissure, from Germanic *klufti-(*klub-ti-).3.glyph, glyptic; anaglyph, hieroglyphic, from Greek gluphein, to carve. 4. Suffixed zero-grade form *glubh-m-.glume, from Latin glma, husk of grain. (Pokorny gleubh- 401.)
ofan, to split, cleave, from Germanic *kleuban. 2. Probably o-grade form *gloubh-. clever, from Middle English cliver, nimble, skillful, perhaps akin to East Frisian klüfer, klifer, skillful, and Old Norse kleyfr, easy to split, from Germanic *klaubri-. 
-. glume, from Latin gl
ma, husk of grain. (Pokorny gleubh- 401.) 
