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

• caudal fin
• caudal vertebra
• caudally
• Caudata
• caudate
• caudate nucleus
• clairvoyant
• clam
• clam chowder
• clam dip
• clam up
• clamant
• Clamato
• Clamatores
• clamatorial
• clambake
• clamber
• clammily
• clamminess
• clammy
• clammy chickweed
• clammy locust
• clammyweed
• clamor
• clamoring