Deny d*** constitutes an oath (7)
I believe the answer is:
disavow
'deny' is the definition.
(I know that disavow is a type of deny)
'd constitutes an oath' is the wordplay.
'constitutes' becomes 'is' ('be' can be a synonym of 'constitute').
'an' becomes 'a'.
'oath' becomes 'vow' (synonyms).
'd'+'is'+'a'+'vow'='DISAVOW'
(Other definitions for disavow that I've seen before include "Refuse to acknowledge" , "Deny responsibility for (something)" , "To deny support" , "To deny knowledge of" , "Disclaim" .)