WordNet
n. a narrow window having a lancet arch and without tracery
Wikipedia
A lancet window is a tall, narrow window with a pointed arch at its top. It acquired the "lancet" name from its resemblance to a lance. Instances of this architectural motif are typical of Gothic ecclesiastical structures of the earliest period. Lancet windows may occur singly, or paired under a single moulding, or grouped in an odd number with the tallest window at the centre.
The motif first appeared in the French early-Gothic period (c. 1140–1200) and later in the English period of Gothic architecture (1200–1275). So common was the lancet window feature that this era is sometimes known as the "Lancet Period".
The term "lancet window" is properly applied to windows of austere form, without tracery. Paired windows were sometimes surmounted by a simple opening such as a quatrefoil cut in plate tracery. This form gave way to the more ornate, multi-light traceried windowed.
Usage examples of "lancet window".
He had been reclining on his bed with his face uplifted to the light from the narrow lancet window, but he swung his feet to the floor and moved hospitably to make way for Cadfael on the pallet beside him.
As she straightened she gazed out through the little lancet window, off across , the lake.
Right-hand stick, left-hand foot, and a landing where a lancet window poured a pearly stain of winter light on the dark wood.
Most wondrous of all was the lancet window set deep in the thick stone wall.
On the fifth day, they even gained access to a narrow lancet window that looked out onto the main courtyard of the bishop's manor.