a.
1.
Hard, harsh, rugged, rough.
2.
Hardened, obstinate, firm, callous, unfeeling, stubborn, unyielding, dogged, pig-headed, inflexible, inexorable, cantankerous, hardhearted, unbending, unsusceptible, insensible.
3.
Depraved, graceless, shameless, reprobate, lost, impenitent, irreclaimable, incorrigible.