Exhaustingly difficult or tiring; requiring extreme effort and endurance over a long period.
From the verb 'gruel,' which came from Old French 'gruel' (thin porridge). Prisoners fed only thin gruel suffered from exhaustion, so the word came to mean any torturous ordeal.
A 'grueling' ordeal is named after gruel—the thin, tasteless porridge fed to prisoners—because eating nothing but gruel left people so weak and exhausted that the word became synonymous with anything that wears you down!
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