1. (Usually thews) Muscle or sinew.
2. (Thews) physical strength.
“Thew” is one of those lean yet powerful words that fits so well into a good action-laden scifi/fantasy story. When muscle and sinew aren’t cutting it and you just need a little something extra, you can always reach for “thew.”
There was a fleeting concussion, a fierce writhing and intertwining of limbs and bodies, and then Conan sprang clear, every thew quivering from the violence of his efforts; blood started where the grazing fingers had torn the skin. In that instant of contact he had experienced the ultimate madness of blasphemed nature; no human flesh had bruised his, but metal animated and sentient; it was a body of living iron which opposed his.
– Robert E. Howard, The Devil in Iron (1934)