Include a religious man (3)
I believe the answer is:
add
'include' is the definition.
(thesaurus)
'a religious man' is the wordplay.
'religious man' becomes 'dd' (abbreviation for Doctor of Divinity degree).
'a'+'dd'='ADD'
(Other definitions for add that I've seen before include "Put together (numbers)" , "Sum up; say further" , "Count up" , "do some mathematics" , "Increase" .)