fastness
/ˈfɑːstnɪs/noun
1
- a secure refuge, especially a place well protected by natural features（尤指受天然地貌保护的）安全处所：
a remote Himalayan mountain fastness.
喜马拉雅山山间的一个僻静去处。
2
- mass noun the ability of a material or dye to maintain its colour without fading or washing away（材料或染料的）色牢度不褪色性：
the dyes differ in their fastness to light.
这些染料在光照下的不褪色性各不相同。
词源
Old English fæstnes （see FAST1 , -NESS）.