Beekes, Etymological Dictionary of Greek (Brill 2010) Treated in Beekes, Etymological Dictionary of Greek (Brill 2010) s.v. θέω (scan pp. 591-592; entry #2560). Root candidates: *dawwa-.
Chantraine, Dictionnaire etymologique de la langue grecque Treated in Chantraine, Dictionnaire etymologique de la langue grecque s.v. θέω (scan p. 447; entry #3134).