Title, fitting one, held by Tory (7)
I believe the answer is:
caption
'title' is the definition.
(caption is a kind of title)
'fitting one held by tory' is the wordplay.
'fitting' becomes 'apt' (I've seen this before).
'one' becomes 'i' (Roman numeral).
'held by' means one lot of letters goes inside another.
'tory' becomes 'con' (abbreviation for Conservative).
'apt'+'i'='apti'
'apti' going inside 'con' is 'CAPTION'.
(Other definitions for caption that I've seen before include "Legend with a photograph" , "Brief description of an illustration" , "accompanying message" , "Explanatory words or heading" , "Explanation of an illustration" .)