punishing vs grueling

punishing and grueling both are adjectives.

Word	Noun	Adjective	Verb	Adverb
punishing	No	Yes	No	No
grueling	No	Yes	No	No

As adjectives, punishing and grueling are synonyms defined as:

punishing and grueling: characterized by effort to the point of exhaustion; especially physical effort

Other synonyms of punishing include arduous, backbreaking, gruelling, hard, heavy, laborious, operose, toilsome.

punishing (adjective)	grueling (adjective)
resulting in punishment	characterized by effort to the point of exhaustion; especially physical effort
characterized by effort to the point of exhaustion; especially physical effort