Sinewy commander? (6)
I believe the answer is:
leader
'commander?' is the definition.
(I've seen this in another clue)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for leader that I've seen before include "One whose example is followed" , "Principal player in an orchestra" , "Party head" , "Important (newspaper) article" , "Pioneer" .)