1. Plural of fastness: a secure or fortified place; a stronghold or fortress.
2. Plural of fastness: the quality or state of being firm, secure, or fixed in place.
Usage: less common usage
3. Plural of fastness: remote, inaccessible, or wild regions or places.

Examples

• The rebels retreated to mountain fastnesses where the army could not easily reach them.
• Medieval castles served as fastnesses against invading forces.
• The bandits hid in the fastnesses of the forest.
• The fortress's fastnesses made it nearly impossible to breach.
• Ancient peoples built their fastnesses on high cliffs for protection.
• The explorer ventured into the fastnesses of the unexplored jungle.