Fruit of theatrical conversation (7)
I believe the answer is:
rhubarb
'fruit' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for rhubarb that I've seen before include "Meaningless talk" , "Vegetable used as fruit" , "Edible stem" , "Word repeated by actors to simulate conversation" , "Rheum rhaponticum" .)