ˈfas(t)nə̇s, -aas-, -ais-, -ȧs- noun
( -es )
Etymology: Middle English fastnesse, from Old English fæstnes, from fæst fast + -nes -ness — more at fast , -ness I
1. : the quality or state of being fast: as
a. : firmness or fixedness : fixed attachment : fixity
b. obsolete : security , inaccessibility
c. : swiftness , speed
d. : resistance to color change : the quality of being colorfast — used of dyes or dyed materials
e. : resistance to the action of certain especially toxic substances (as that developed by some organisms)
2. obsolete : density , solidity
3.
a. : a fortified or secure place : stronghold , fort , fortress , castle
b. : a place of retreat or privacy
visited them in their desert fastness — Simon Bourgin
the poet can retire into the fastness of himself — Clifton Fadiman
— often used in plural
into the fastnesses of the pine- and oak-covered hills — American Guide Series: Tennessee
down in the remote fastnesses of Staten Island — Richard Burke