Tommy’s secret (7)
I believe the answer is:
private
This clue is a double definition.
'tommy's' is the first definition.
(thesaurus)
'secret' is the second definition.
('private' can be similar in meaning to 'secret')
(Other definitions for private that I've seen before include "Soldier; personal" , "Army rank; secluded" , "Secret sort of soldier" , "Secret - soldier of the lowest rank" , "Secret, not public" .)