It has been generally accepted that the Greek word θ vατos and its kin are to be connected etymologically with a few scattered words in other Indo-European branches, as follows: Skt. root dhvan: ádhvanῑt (aor.; RV 626.13), ádhvānayat (impf. caus.; RV 459.10), dhvanayῑt (aor. caus.; 162.15), dhvāntá- (ptc.; 899.2, 11, 939.7); ⁈sich verhüllen, erlöschen, schwinden, s'éteindre’, caus. ‘einhüllen, schwärzen', ptc. ‘dunkel, enveloppö, sombre’.
Roland G. Kent (Sun,) studied this question.