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

• insatiableness
• insatiably
• insatiate
• inscribe
• inscribed
• inscriber
• inscription
• inscriptive
• inscriptively
• inscrutability
• inscrutable
• inscrutableness
• inscrutably
• inseam
• insect
• insect bite
• insect powder
• insect repellant
• insect repellent
• Insecta
• insectan
• insecticidal
• insecticidally
• insecticide
• insectifuge