The Two Ronnies initially leaving soup (4)
I believe the answer is:
both
'the two' is the definition.
(synonyms)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for both that I've seen before include "Each of two (alternatives)" , "The one and the other" , "couple" , "The two (things)" , "Two considered together" .)