A fichu (pronounced fish-oo) is a lightweight triangular scarf worn by a woman; a large, square kerchief, folded diagonally into a triangle, worn by women from the 18th century to fill in the low neckline of a bodice; a draped scarf or shawl worn around shoulders and tied in a knot at breast, with ends hanging down loosely.
(This picture is from an excellent site explaining the differences of various pieces of millinery can be found here.)
