Fastness (noun)

1. The quality of being firm and unchanging.
2. The quality of being securely fixed in place.
3. The quality of being difficult to move or change.

Origin:

Middle english: from old english fæstness, from fæst 'fast, firm'.

Examples:

1. The fastness of the rock cliffs makes them an ideal habitat for seabirds.
2. The fastness of the old castle's walls was its greatest defense against invaders.
3. The company prides itself on the fastness of its production processes.
4. The fastness of the bond between the mother and child is unbreakable.
5. The fastness of the ship's anchor kept it from drifting away in the storm.