1.  punishing(a = adj.ppl) - resulting in punishment; "the king imposed a punishing tax"

2.  punishing(s = adj.all) arduous, backbreaking, grueling, gruelling, hard, heavy, laborious, operose, toilsome - characterized by effort to the point of exhaustion; especially physical effort; "worked their arduous way up the mining valley"; "a grueling campaign"; "hard labor"; "heavy work"; "heavy going"; "spent many laborious hours on the project"; "set a punishing pace"

N  punishment, punition, chastisement, chastening, correction, castigation, discipline, infliction, trial, judgment, penalty, retribution, thunderbolt, Nemesis, requital, penology, retributive justice, lash, scaffold, imprisonment, transportation, banishment, expulsion, exile, involuntary exile, ostracism, penal servitude, hard labor, galleys, beating, flagellation, fustigation, gantlet, strappado, estrapade, bastinado, argumentum baculinum, stick law, rap on the knuckles, box on the ear, blow, stripe, cuff, kick, buffet, pummel, slap, slap in the face, wipe, douse, coup de grace, torture, rack, picket, picketing, dragonnade, capital punishment, execution, lethal injection, the gas chamber, hanging, electrocution, rail-riding, scarpines, decapitation, decollation, garrotte, garrotto, crucifixion, impalement, firing squad, martyrdom, auto-da-fe, noyade, happy dispatch, hara-kiri, seppuku, drinking the hemlock, punishing, penal, punitory, punitive, inflictive, castigatory, punished, Int, a la lanterne!, culpan paena premit comes, eating the bitter bread of banishment, gravis ira regum est semper, sera tamen tacitis paena venit pedibus, suo sibi gladio hunc jugulo.