Of a fortress or other stronghold: that may be taken by force; vulnerable to attack. Now chiefly in extended use.

(un-, prefix1 affix 2.)

That may be taken by force, conquered, or overcome.

†Unwalled. (See immure, v. 1.)

That can be taken by storm.

Without a fortification; unfortified.

Of places, etc.: Open to attack or assault by armed forces; liable to be taken or entered in this way.