fastness

From Middle English fastnes, fastnesse (“immovableness, stability; firmness, solidness; secure attachment; constancy; obstinacy; something giving firmness or strength; of sleep: soundness; of a wound: healing; assurance, confirmation”) [and other forms], from Old English fæstnes (“fastness, firmness, stability; resolution; tenacity; vigour; firmament; fortification”) [and other forms], from fæst (“firm, stable; constant”) (from Proto-Germanic *fastuz (“firm, fixed; secure”); see further at that entry) + -nes (suffix forming abstract nouns denoting a quality or state). The English word may be analysed as fast + -ness.