"punishing" in the verb sense

1. punish, penalize, penalise

impose a penalty on inflict punishment on

"The students were penalized for showing up late for class"

"we had to punish the dog for soiling the floor again"

"punishing" in the adjective sense

1. punishing

resulting in punishment

"the king imposed a punishing tax"

2. arduous, backbreaking, grueling, gruelling, hard, heavy, laborious, operose, punishing, 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"

Source: WordNet® (An amazing lexical database of English)

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