The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
Appendix I
Indo-European Roots
ENTRY:
to-
DEFINITION:
Demonstrative pronoun. For the nominative singular see so-. Derivatives include decoy, thus, and tandem. 1a.the2; natheless, from Old English th,th (instrumental case), by the; b.decoy, from Middle Dutch de, the; c.lest, from Old English the, a conjunction. ac from Germanic *th, from Indo-European instrumental form *t.2.though, from Middle English though, though, from a Scandinavian source akin to Old Norse th, though, from Germanic *thauh, for all that. 3.these, this, those, from Old English thes,this, this, from Germanic *thasi-.4.than, then, from Old English thanne,thænne,thenne, than, then, from Germanic *thana-.5.thence, from Old English thanon, thence, from Germanic *thanana-.6.there, from Old English thr,thr, there, from Germanic *thr.7.thither, from Old English thæder,thider, thither, from Germanic *thathro.8.they, from Old Norse their, they, from Germanic nominative plural *thai.9.their, from Old Norse their(r)a, theirs, from Germanic genitive plural *thaira.10.them, from Old Norse theim and Old English thm, them, from Germanic dative plural *thaimiz.11. Extended neuter form *tod-.that, from Old English thæt, that, from Germanic *that.12.thus, from Old English thus, thus, from Germanic *thus-.13. Adverbial (originally accusative) form *tam.tandem, tantamount, from Latin tandem, at last, so much, and tantus, so much. 14. Suffixed reduced form *t-li-.tales, from Latin tlis, such. 15. tauto-, from Greek to, the. (Pokorny 1. to- 1086.)