• IPA: /ˈfæstnəs/, [ˈfæsnəs]
• (trap–bath split) IPA: /ˈfɑːstnəs/, [ˈfɑːsnəs]

fastness

1. A secure or fortified place; a stronghold, a fortress.
   • 1611, John Speed, The History of Great Britaine under the Conquests of the Romans, Saxons, Danes and Normans, London, Book 9, Chapter 9, p. 528,

     [...] if the Welsh compelled by famine ventred out of their strengthes or fastnesses, in or about Snowdon, the Garrison Souldiers of Gannocke were ready to intercept and kill them [...]

   • 1803, John Browne Cutting, “A Succinct History of Jamaica” in Robert Charles Dallas, The History of the Maroons, London: Longman and Rees, Volume 1, p. xxxviii,

     [...] the slaves that yet remained in the fastnesses of Jamaica, attached to the Spanish, and hostile to the English settlers, continued to be troublesome, and at times formidable.

   • 1912 February–July, Edgar Rice Burroughs, “Under the Moons of Mars”, in The All-Story, New York, N.Y.: Frank A. Munsey Co., OCLC 17392886 ↗; republished as “Child-raising on Mars”, in A Princess of Mars, Chicago, Ill.: A[lexander] C[aldwell] McClurg & Co., 1917, OCLC 419578288 ↗, page 69 ↗:

     The incubators are built in remote fastnesses, where there is little or no likelihood of their being discovered by other tribes.

   • 1919, W[illiam] Somerset Maugham, chapter IV, in The Moon and Sixpence. A Novel, London: William Heinemann, OCLC 563525353 ↗; The Moon and Sixpence, 1st American edition, [New York, N.Y.]: Grosset & Dunlap Publishers by arrangement with George H. Doran Company, 1919, OCLC 365836 ↗, page 26 ↗:

     When she came to know writers it was like adventuring upon a stage which till then she had known only from the other side of the footlights. She saw them dramatically, and really seemed herself to live a larger life because she entertained them and visited them in their fastnesses.

2. The state of being fast.
   1. Firmness, security.
   2. Rapidity, swiftness.
3. The ability of a dye to withstand fading.

• Russian: кре́пость