Seed in banana republic to enter Wimbledon, finally (5)
I believe the answer is:
acorn
'seed' is the definition.
(I've seen this before)
'banana republic to enter wimbledon finally' is the wordplay.
'finally' says to take the final letters.
The final letters of 'banana republic to enter wimbledon' are 'ACORN'.
'in' acts as a link.
(Other definitions for acorn that I've seen before include "fruit in a cup" , "From which a tall tree may grow" , "Might source" , "from which something bigger may develop" , "Fruit-seed of the oak" .)