fortress

Early 14 c., from Old French forteresce, forteresse, forterece (“strong place, fortification”) [from 12th c.], variant of fortelesse, from Medieval Latin fortalitia, from Latin fortis (“strong”) (see fort) +‎ -itia, added to adjectives to form nouns of quality or condition. French -ess, from Latin -itia is also in words such as duress, largesse and riches. For change of medial -l- to -r- in Old French, compare orne (“elm”) from ulmus; chartre from cartula and chapitre from capitulum.

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IPA^(key): /ˈfɔɹ.tɹəs/

fortress (plural fortresses)

1. A fortified place; a large and permanent fortification, sometimes including a town; for example a fort, a castle; a stronghold; a place of defense or security.
2. (chess) A position that, if obtained by the weaker side, will prevent penetration by the opposing side, generally achieving a draw.

• fortalice, fortilice

fortress (third-person singular simple present fortresses, present participle fortressing, simple past and past participle fortressed)

1. (transitive) To furnish with a fortress or with fortresses; to guard, to fortify.
   • 1594, William Shakespeare, Lvcrece (First Quarto)‎, London: Printed by Richard Field, for Iohn Harrison, […], OCLC 236076664:

     Honour and Beautie in the owners armes, / Are weaklie fortreſt from a world of harmes.