Fort, n.
Etymology: [F., from fort strong, L. fortis; perh. akin to Skr. darh to fix, make firm, and to E. firm Cf. Forte, Force, Fortalice, Comfort, Effort.]
(Mil.)
A strong or fortified place; usually, a small fortified place, occupied only by troops, surrounded with a ditch, rampart, and parapet, or with palisades, stockades, or other means of defense; a fortification. Detached works, depending solely on their own strength, belong to the class of works termed forts. Farrow.
Shades of meaning
Fernald has no entry of its own for fort; he lists it under fortification.
Where he writes about it:
Fortification is the general word for any artificial defensive work; a fortress is a fortification of especial size and strength; a fortress is regarded as permanent, and is ordinarily an independent work; a fort or fortification may be temporary; a fortification may be but part of a defensive system; we speak of the fortifications of a city. — from fortification
Fort is the common military term for a detached fortified building or enclosure of moderate size occupied or designed to be occupied by troops. — from fortification
Antonyms
none given