From WordNet (r) 2.0 (August 2003) [wn]:
observatory
n 1: a building designed and equipped to observe astronomical
phenomena
2: a structure commanding a wide view of its surroundings [syn:
lookout, observation tower, lookout station]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Observatory \Ob*serv"a*to*ry\, n.; pl. Observatories. [Cf. F.
observatoire.]
1. A place or building for making observations on the
heavenly bodies.
[1913 Webster]
The new observatory in Greenwich Park. --Evelyn.
[1913 Webster]
2. A building fitted with instruments for making systematic
observations of any particular class or series of natural
phenomena.
[1913 Webster]
3. A place, as an elevated chamber, from which a view may be
observed or commanded.
[1913 Webster]
4. (Mil.) A lookout on a flank of a battery whence an officer
can note the range and effect of the fire; usually
referred to as an observation post. --Farrow.
[1913 Webster +PJC]