The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
Appendix I
Indo-European Roots
ENTRY:
dhghem-
DEFINITION:
Earth. Oldest form *dhhem-, becoming *dhghem- in centum languages. Derivatives include bridegroom, chameleon, and homicide. 1. Suffixed zero-grade form *(dh)gh-on-, “earthling.” bridegroom, from Old English guma, man, from Germanic *gumn-.2. O-grade form *dh(e)ghom-.chthonic; autochthon, from Greek khthn, earth. 3. Zero-grade form *dhgh-.chamaephyte, chameleon, chamomile, germander, from Greek khamai, on the ground. 4. Suffixed o-grade form *(dh)ghom-o-.humble, humiliate, humility, humus1, omerta; exhume, inhume, transhumance, from Latin humus, earth. 5. Suffixed o-grade form *(dh)ghom-on-, “earthling.” a.homage, hombre1, hominid, homo1, homunculus, ombre; bonhomie, homicide, from Latin hom, human being, man; b.human, humane, from Latin hmnus, human, kind, humane (in part from dhghem-). 6. Suffixed form *(dh)ghem-y-.chernozem, sierozem, zemstvo, from Old Russian zem, land, earth. 7. Full-grade form *(dh)ghem-.zamindar, from Persian zamn, earth, land. (Pokorny hem- 414.)
hem-, becoming *dhghem- in centum languages. 
-on-, “earthling.” bridegroom, from Old English guma, man, from Germanic *gum
n-. 2. O-grade form *dh(e)ghom-. chthonic; autochthon, from Greek khth
m
nus, human, kind, humane (in part from dhghem-). 6. Suffixed form *(dh)ghem-y
, land, earth. 7. Full-grade form *(dh)ghem-. zamindar, from Persian zam
n, earth, land. (Pokorny 
em- 414.) 
