The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
Appendix I
Indo-European Roots
ENTRY:
ko-
DEFINITION:
Stem of demonstrative pronoun meaning “this.” Oldest form *o-, becoming *ko- in centum languages. Derivatives include he1, et cetera, and behind. I. Variant form *ki-.1a.he1, from Old English h, he; b.him, from Old English him, him (dative of h); c.his, from Old English his, his (genitive of h); d.her, from Old English hire, her (dative and genitive of heo, she); e.it, from Old English hit, it (neuter of h); f.here, from Old English hr, here; g.hence, from Old English heonane,heonon, from here. a–g all from Germanic *hi-.2. Suffixed form *ki-tro-.hither, from Old English hider, hither, from Germanic *hi-thra-.3. Suffixed form *ki-s. cis-, from Latin cis, on this side of. II. Variant form *ke-.1. Preposed in *ke-etero- (*e-tero-, a second time, again; see i-). et cetera, from Latin cterus (neuter plural ctera), the other part, that which remains. 2. Postposed in Latin -ce (see nu-). III. 1.behind, hind1, from Old English behindan, in the rear, behind (bi, at; see ambhi). 2.hinterland, from Old High German hintar, behind. 3.hinder1, hindrance, from Old English hindrian, to check, hinder, from Germanic derivative verb *hindrn, to keep back. 1–3 all from Germanic root *hind-, behind, attributed by some to this root (but more likely of obscure origin). (Pokorny 1. ko- 609.)
o-, becoming *ko- in centum languages. 
, he; b. him, from Old English him, him (dative of h
n, to keep back. 1–3 all from Germanic root *hind-, behind, attributed by some to this root (but more likely of obscure origin). (Pokorny 1. ko- 609.) 
