refractory (adj.)

"stubborn, obstinate, perverse," 1610s (earlier refractorious, 1550s, refractary, c. 1600), from Latin refractarius "obstinate, stubborn," from past participle stem of refringere "to break up" (see refraction). The notion is said to be "breaking back" all attempts to enforce obedience. Related: Refractorily; refractoriness.