Where does “fastnesse” come from?

fastnesse (Middle English) comes from Old English fæstnes, from Old English -nes, from Proto-West Germanic -nassī, from Proto-Germanic -inassuz, from Proto-West Germanic -ī, from Proto-Germanic -į̄, from Proto-Indo-European -íh₂, from Proto-Indo-European -h₂ — Creates collective nouns, which refer to groups...

Ancestry of “fastnesse”, step by step

fastnesse traces back through two separate lines of ancestry.

via Old English fæstnes

StepLanguageWordMeaning
1Old Englishfæstnesfastness, firmness, firmament, fortification,...
2Old English-nesUsed to form abstract nouns, usually from...
3Proto-West Germanic-nassīUsed to form abstract nouns, usually from...
4Proto-Germanic-inassuz-ness
5Proto-West Germanic-ī-ness, -th
6Proto-Germanic-į̄-th
7Proto-Indo-European-íh₂—
8Proto-Indo-European-h₂Creates collective nouns, which refer to groups...

via Old English fæstnis

StepLanguageWordMeaning
1Old Englishfæstnisfirmness; stronghold; firmament

Words derived from “fastnesse”

Every word from Proto-Indo-European -h₂ →Every word from Old English -nes →Every word from Proto-Germanic -į̄ →