Watch one dining after theatre (8)
I believe the answer is:
repeater
'watch' is the definition.
(thesaurus)
'one dining after theatre' is the wordplay.
'one dining' becomes 'eater' (someone eating a meal).
'after' is a charade indicator (letters next to each other).
'theatre' becomes 'rep' (repertory theatre).
'eater' put after 'rep' is 'REPEATER'.
(Other definitions for repeater that I've seen before include "Watch - gun" , "teller" , "habitual criminal" , "Handgun able to fire again without reloading" , "it's dangerous" .)