Webster's Revised Unabridged Dictionary · 1913

diehard

diehard (dī"hard`) , noun

1.
one who stubbornly adheres to traditional and outdated views.
2.
one who vigorously defends an apparently hopeless position, a lost cause, etc.

diehard (dī"hard`) , adjective

stubbornly and vigorously resisting in the face of seemingly hopeless odds; as, diehard opposition.