blockhouse

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A military fortification constructed of sturdy material, such as concrete, and designed with ports for defensive firing or observation.
• noun A heavily reinforced building used for launch operations of missiles and space launch vehicles.
• noun A fort made of squared timbers with a projecting upper story.

from The Century Dictionary.

• noun Originally, a detached fort blocking the access to a landing, a mountain pass, narrow channel, etc.; in later use, an edifice of one or more stories, constructed chiefly of hewn timber, and supplied with loopholes for musketry and sometimes with embrasures for cannon.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Mil.) An edifice or structure of heavy timbers or logs for military defense, having its sides loopholed for musketry, and often an upper story projecting over the lower, or so placed upon it as to have its sides make an angle wit the sides of the lower story, thus enabling the defenders to fire downward, and in all directions; -- formerly much used in America and Germany.
• noun West. & South. U. S. A house of squared logs.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A sturdy military fortification, often of concrete, with gunports.
• noun A reinforced building from which to control hazardous operations, such as an explosion or a rocket launch.
• noun dated A temporary wooden fortification with a projecting upper story.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a stronghold that is reinforced for protection from enemy fire; with apertures for defensive fire