punishing
1. [ adjective ] resulting in punishment
Examples:

"the king imposed a punishing tax"

Related terms: punish
2. [ adjective ] characterized by toilsome effort to the point of exhaustion; especially physical effort
Synonyms: hard arduous labourious gruelling heavy laborious grueling toilsome backbreaking
Examples:

"worked their arduous way up the mining valley" "a grueling campaign" "hard labor" "heavy work" "heavy going" "spent many laborious hours on the project"

Related terms: effortful
Similar spelling:   punishingly
  punching_bag
  punishment