Thews refers to muscular power or strength. It also means muscles or sinews. Thews finds its roots in Middle English (spoken in the late 11th century through the late 15th century), where theawes meant good physical qualities or strength.
What are thews (from Ivanhoe)?
If you want to use it as an adjective, try these: thewy, thewier, thewiest.
In Ivanhoe, the Black Knight is surprised to see how hale and hearty the Clerk of Copmanhurst is, compared to other ascetic holy men of that time. Little does the Black Knight know that the Clerk is really Friar Tuck (of Robin Hood's band):
I cannot but marvel that a man possessed of such thews and sinews as thine, and who therewithal shows the talent of so goodly a trencher-man, should think of abiding by himself in this wilderness. In my judgment, you are fitter to keep a castle or a fort, eating of the fat and drinking of the strong, than to live here upon pulse and water . . .