arduous /ärˈdū-əs/

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

• threefoldness
• threefoldnesses
• three-foot
• three-four
• three-four time
• three-halfpence
• three-halfpenny
• three-halfpennyworth
• three-halfpennyworths
• three-handed
• threeha'porth
• three-jaw chuck
• three-jaw chucks
• three kings of Cologne
• three-leafed
• three-leaved
• three-legged
• three-line whip
• three-man
• three-masted
• three-master
• three-masters
• three-mile limit
• three-mile limits
• three-monthlies