hardmouthed

[hahrd-mouth d, -moutht]

adjective

of or relating to a horse not sensitive to the pressure of a bit.
stubborn; obstinate; self-willed.

Origin of hardmouthed

First recorded in 1610–20; hard + mouth + -ed3
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019