(1):

(n.) Formerly, a starting derrick (the use of which is now abandoned) for an aeroplane.

(2):

(n.) A low tower, having a truncated pyramidal form, and flanking an ancient Egyptian gateway.

(3):

(n.) An Egyptian gateway to a large building (with or without flanking towers).

(4):

(n.) A tower, commonly of steelwork, for supporting either end of a wire, as for a telegraph line, over a long span.

(5):

(n.) A post, tower, or the like, as on an aerodrome, or flying ground, serving to bound or mark a prescribed course of flight.