Available Definitions:
1) n. - A place or building for making observations on the heavenly bodies.
2) n. - A building fitted with instruments for making systematic observations of any particular class or series of natural phenomena.
3) n. - A place, as an elevated chamber, from which a view may be observed or commanded.
4) n. - A lookout on a flank of a battery whence an officer can note the range and effect of the fire.