arduous /ärˈdū-əs/

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

• plenilune
• plenilunes
• plenipo
• plenipoes
• plenipos
• plenipotence
• orthographical
• orthographically
• orthographies
• orthographist
• orthographists
• orthographs
• orthography
• orthokeratology
• orthologous
• orthologue
• orthologues
• orthomorphic
• orthopaedic
• orthopaedical
• orthopaedically
• orthopaedics
• orthopaedist
• orthopaedists
• orthopaedy