A vow from dowagers with no God (5)
I believe the answer is:
swear
'a vow' is the definition.
(thesaurus)
'from dowagers with no god' is the wordplay.
'from' indicates anagramming the letters (from the letters).
'with no' suggests deleting specific letters.
'dowagers' with 'god' taken out is 'waers'.
'waers' anagrammed gives 'SWEAR'.
(Other definitions for swear that I've seen before include "Vow, attest" , "Eff and blind" , "Assert" , "Express annoyance" , "Utter obscenities or take an oath" .)