The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
Appendix I
Indo-European Roots
ENTRY:
so-
DEFINITION:
This, that (nominative). For other cases see to-. 1.the1, from Late Old English the, masculine demonstrative pronoun, replacing se (with th- from oblique forms; see to-). 2.hoi polloi, from Greek ho, the. 3. Feminine form *sy-.she, from Old English so,se, she, from Germanic *sj.4. Compound variant form *sei-ke (*-ke, this; see ko-). sic1, from Latin sc, thus, so, in that manner. (Pokorny so(s) 978.)