( especially BrE ) ( NAmE usually gruel·ing ) / ˈgruːəlɪŋ; NAmE / adjective
very difficult and tiring, needing great effort for a long time
SYN punishing :
a gruelling journey / schedule
I've had a gruelling day.
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WORD ORIGIN
mid 19th cent.: from the verb gruel exhaust, punish , from an old phrase get one's gruel receive one's punishment .