What is the origin of the word gazebo?

/g'zi:beu/ a small building, usually in a garden, with a good view.
Early gazebos were often a tower or lantern on the roof of a house, a projecting balcony, or a structure attached to the top of a wall. Only much later was the word applied to a summerhouse, usually one with open sides. To be strict about it, only those edifices with a good view may be given that name; all others are mere shelters.
For more on the entymology of 'gazebo', see Michael Quinion's World Wide Words