arduous /ärˈdū-əs/

1. Steep, difficult to climb
2. Difficult to accomplish
3. Laborious

• black breads
• black-browed
• black bryony
• blackbuck
• blackbucks
• black-bully
• black bun
• black buns
• black butt
• black cabbage
• black cap
• blackcap
• blackcaps
• black carbon
• black-cat
• black-cats
• black cattle
• black chalk
• black clergy
• black-coated
• blackcock
• blackcocks
• black coffee
• Black Consciousness
• Black Country