1. Incapable of being ascended
   - unscalable 
2. Incapable of being surmounted or climbed
   - unsurmountable

See also: impassable, unpassable

• Outaouais
• outargue
• outback
• outbalance
• outbid
• outboard
• outboard motor
• outboard motorboat
• outbound
• outbrave
• outbreak
• outbred
• outbuilding
• outburst
• outcall
• outcast
• outcaste
• outclass
• outclassed
• outcome
• outcrop
• outcropping
• outcry
• outdated
• outdistance