Definition of sinews:
(n) :
(figuratively) Muscular power, muscle; nerve, nervous energy; vigor, vigorous strength.
(n) :
(figuratively, often in the plural) That which gives strength or in which strength consists; a supporting factor or member; mainstay.
(n) :
(anatomy) A cord or tendon of the body.
(n) :
A cord or string, particularly (music) as of a musical instrument.
(v) :
(transitive) To knit together or make strong with, or as if with, sinews.
(n) :
(anatomy, obsolete) A nerve.