Prisoner drinking a pint with international legend (7)
I believe the answer is:
caption
'legend' is the definition.
(synonyms)
'prisoner drinking a pint with international' is the wordplay.
'prisoner' becomes 'con' (abbreviation for 'convict').
'drinking' indicates putting letters inside (inserted letters are consumed or drunk).
'pint' becomes 'pt' (abbreviation).
'with' is a charade indicator (letters next to each other).
'international' becomes 'i' (abbreviation eg in IMF).
'a'+'pt'+'i'='apti'
'con' going around 'apti' is 'CAPTION'.
(Other definitions for caption that I've seen before include "Brief description of an illustration" , "Provide (a picture) with a title" , "Explanation of an illustration" , "Text under photo" , "Pontiac (anag)" .)