Mulishness, 8 letters
Resoluteness by virtue of being unyielding and inflexible, 8 letters
Bull-headed, 8 letters
Dogged, 8 letters
Hard, 8 letters
Hardhearted, 8 letters
Inflexible, 8 letters
Intractable, 8 letters
Stubborn, 8 letters
Stubborn as a mule, 8 letters
Unbending, 8 letters
Unyielding, 8 letters