so
Middle English
From Middle English so, swo, zuo, swa, swe, from Old English swā, swǣ, swē (“so, as, the same, such, that”), from Proto-West Germanic *swā, from Proto-Germanic *swa, *swē (“so”), from Proto-Indo-European *swē, *swō (reflexive pronomial stem). Cognate with Scots sae (“so”), Saterland Frisian so (“so”), West Frisian sa (“so”), Dutch zo (“so”), German Low German so (“so”), German so (“so”), Danish så (“so”), Norwegian Nynorsk so (“so”), Swedish så (“so, such that”), Faroese so (“so”), Icelandic svo (“so”), Old Latin suad (“so”), Albanian sa (“how much, so, as”), Ancient Greek ὡς (hōs, “as”), Urdu سو (sō, “hence”).
so that
Middle English
From Middle English so that, so þat, sa þat, swo þat, swa þat, from Old English swā þæt, equivalent to so + that. Cognate with Saterland Frisian sodät, West Frisian sadat, Dutch zodat, German sodaß, sodass.