Theatrical waiter could be on stage with a bit of rehearsal (8)
I believe the answer is:
estragon
'theatrical waiter' is the definition.
(character in the play Waiting for Godot)
'could be on stage with a bit of rehearsal' is the wordplay.
'could be' is an anagram indicator.
'with' means one lot of letters goes inside another.
'a bit of' suggests taking the first letters.
The first letter of 'rehearsal' is 'r'.
'on'+'stage'='onstage'
'onstage' with letters rearranged gives 'estagon'.
'estagon' enclosing 'r' is 'ESTRAGON'.
(Other definitions for estragon that I've seen before include "Character of play" , "Vladimir's fellow-waiter" , "Waiter" .)