Roux

A French/English dictionary will tell you that this word means a redhead. But as every housewife over 60 knows, a roux is that magic mix of equal parts flour and butter heated together (long enough to lose its floury taste) that constitutes the basis of many sauces including Béchamel and its derivatives (Mornay, Soubise etc.). Used for veloutés, thickening gravy and rescuing a watery stew.