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

See also: effortful

• colpoxerosis
• colt
• coltan
• colter
• coltish
• coltsfoot
• Coluber
• Coluber constrictor
• Coluber constrictor flaviventris
• Coluber hippocrepis
• colubrid
• colubrid snake
• Colubridae
• Colubrina
• colubrine
• colugo
• Columba
• Columba fasciata
• Columba livia
• Columba palumbus
• columbarium
• columbary
• Columbia
• Columbia River
• Columbia tiger lily