a large fortified place; a fort or group of forts, often including a town; citadel.
2.
any place of exceptional security; stronghold.
Origin: 1300–50; Middle English forteresse < Old French < Vulgar Latin *fortaricia (compare Medieval Latin fortalitia), equivalent to Latin fort(is) strong + -ar-, formative of uncertain meaning +-icia-ice
early 14c., from O.Fr. forteresse "strong place," variant of fortelesse, from M.L. fortalitia, from L. fortis "strong" + Eng. -ess, a fairly uncommon suffix (duress, largess being other examples), from L. -itia, forming nouns of quality or condition.