nappe /nap 
/ ▸ noun 1 Geology a sheet of rock that has moved sideways over neighbouring strata as a result of an overthrust or folding. 2 Cooking the desired consistency of a sauce, at which it is thick enough to coat the back of a spoon: it is made from a roux and milk, gently simmered and stirred until thickened to a nappe.
– ORIGIN late 19th century: French.
EnglishOxford Dictionary of English
