pun ‧ ish ‧ ing /ˈpʌnɪʃɪŋ/ BrE AmE adjective [usually before noun]
[ Word Family: adjective : ↑ punishable , ↑ punishing , ↑ unpunished , ↑ punitive ; verb : ↑ punish ; noun : ↑ punishment ]
difficult, tiring, or extreme:
He set himself a punishing schedule of conferences.
a series of punishing defeats
a punishing exercise regime