gruel 'to punish' (1800-1900), from gruel 'food'; because people were given gruel as a punishment
gru‧el‧lingBritish English; grueling American English
very difficult and tiring:
The cast took a break from their gruelling schedule.
a grueling journey
WORD FOCUS: difficult WORD FOCUS: difficult difficult to do:hard, tough, challenging, daunting difficult and needing a lot of physical effort:tough, strenuous, back-breaking, gruelling, arduous, punishing difficult to deal with or talk about:tricky, awkward, delicate, sensitive, touchy words for describing a difficult person:awkward, trying words for describing difficult conditions:adverse, hostile ➔ See alsodifficult
Definition from the Longman Dictionary of Contemporary English Advanced Learner's Dictionary.