【Window】 , 【casement】 ,  【dormer】 ,  【oriel】  can mean an opening in the wall of a building that is usually covered with glass and serves to admit light and air.

【Window】 is the ordinary general term for the entire structure, including both its framework and the glass or the movable sashes which that framework encloses.

【Casement】  basically denotes a 【window】 sash attached to one of the upright sides of the frame by hinges; in ordinary use, however, the term is applied to a 【window】 or a series of windows (sometimes called  【casement】 【window】 ) with sashes of this character.

【Dormer】  denotes a 【window】 which stands out from a sloping roof and is typically enclosed by a gable-topped structure.

An  【oriel】  differs from a 【dormer】 in projecting from a wall of a building rather than from a roof, in being at least three-sided and usually either semihexagonal or semisquare in shape, and in being supported by a corbel or bracket rather than by a rafter.