From Middle English tho, tha, from Old English þā ("the, those"), from Proto-Germanic *þai ("those"), from Proto-Indo-European *to-, *só. Cognate with Saterland Frisian do ("the").
From Middle English tho, tha, from Old English þā ("then, when"), from Proto-Germanic *sa ("that"), from Proto-Indo-European *to-, *só. See also German da.