n.

1. 牢固；（顏色）不褪色[U]
   We guarantee the fastness of these dyes.

   我們擔保這些顏料不褪色。

2. 據點；堡壘[C]
   The rebels have withdrawn to their mountain fastness for the winter.

   叛軍撤至他們的山寨過冬。

n.

1. a secure place well protected by natural features.
2. the ability of a dye to maintain its colour without fading or washing away.