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

See also: effortful, toilsomeness

• blushing
• blushing mushroom
• blushingly
• bluster
• blusterer
• blustering
• blusterous
• blustery
• Blériot
• bm
• BMDO
• BMI
• BMR
• BMus
• bn
• BNP
• BNS
• Bo Hai
• bo tree
• bo's'n
• boa
• boa constrictor
• Boann
• boar
• boar thistle