This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

n. The condition or quality of being fast, especially:

n. Firmness; security.

n. Rapidity; swiftness.

n. The quality or condition of color retention; colorfastness.

n. A secure or fortified place; a stronghold.

n. A remote, secret place.

n. A secure or fortified place; a stronghold, a fortress

n. The state of being fast.

n. The ability of a dye to withstand fading

n. The state of being fast and firm; firmness; fixedness; security; faithfulness.

n. A fast place; a stronghold; a fortress or fort; a secure retreat; a castle.

n. Conciseness of style.

n. The state of being fast or swift.

n. The state of being fast and firm or fixed; firm adherence.

n. Strength; security.

n. A stronghold; a fortress or fort; a fortified place; a castle.

n. . Closeness or conciseness, as of style.

n. The state or quality of being fast, in any sense.

n. Synonyms Speed, Swiftness, etc. See quickness.

n. the quality of being fixed in place as by some firm attachment

n. a rate (usually rapid) at which something happens

n. a strongly fortified defensive structure

"But fastness is nothing unless you have accuracy too."

firmness    fixedness    security    faithfulness    stronghold    castle   

fast   

vastness   

solitudes    stronghold    mountain-top    citadel    Highlands    donjon    pagoda    glen    watchtower    muniment