Wines develop strength (5)
I believe the answer is:
sinew
'strength' is the definition.
(I know that sinew is a type of strength)
'wines develop' is the wordplay.
'develop' is an anagram indicator.
'wines' with letters rearranged gives 'SINEW'.
(Other definitions for sinew that I've seen before include "Tendon, for example" , "Inelastic tissue" , "power source" , "fibre" , "Tendon - ligament" .)