Definition of "crenellation"
noun
countable and uncountable, plural crenellations
(countable, uncountable) A pattern along the top of a parapet (fortified wall), most often in the form of multiple, regular, rectangular spaces in the top of the wall, through which arrows or other weaponry may be shot, especially as used in medieval European architecture.
Quotations
This villa was long and low and white, and severe after its manner : for upon and about it were none of those playful ebullitions of taste, such as conical towers, domed roofs, embattlements, statues, coloured tiles and crenellations, such as are dear to architects of villas all the world over.
1922, Michael Arlen, “3/6/1”, in “Piracy”: A Romantic Chronicle of These Days