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

• photopic vision
• photopigment
• photoplate making
• photoreceptor
• photoretinitis
• photosensitise
• photosensitive
• photosensitivity
• photosensitize
• photoshop
• photosphere
• photospheric
• photostat
• Photostat machine
• photosynthesis
• photosynthesise
• photosynthesize
• photosynthetic
• phototaxis
• phototherapy
• phototrophic bacteria
• phototropic
• phototropic bacteria
• phototropism
• photovoltaic