Wines mixed as source of strength (5)
I believe the answer is:
sinew
'source of strength' is the definition.
(I've seen this before)
'wines mixed' is the wordplay.
'mixed' indicates an anagram.
'wines' is an anagram of 'SINEW'.
'as' acts as a link.
(Other definitions for sinew that I've seen before include "Strength; tendon" , "Tough connective tissue" , "Tendon - ligament" , "As synonym for 'strength'" , "power source" .)