1. Characterized by effort to the point of exhaustion; especially physical effort
   "a gruelling campaign"
   - arduous, backbreaking, grueling [US], hard, heavy, laborious, operose, punishing, toilsome

See also: effortful

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• brainish
• brainless
• brainpan
• brainpower
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• brainsick
• brainstem
• brainstorm
• brainstorming
• brainwash
• brainwashed
• brainwashing
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• braise
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• brake
• brake band
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• brake drum
• brake failure