Wimbledon unit (3)
I believe the answer is:
set
'wimbledon unit' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for set that I've seen before include "Become fixed or solid" , "Solidify; group" , "Become stiff like jelly" , "Fix; lay" , "Cake < , plonk < , something served" .)