The word crewel comes from an ancient word describing the curl in the staple, the single hair of the wool. Crewel wool has a long staple; it is fine and can be strongly twisted.
The crewel technique is not a counted-thread embroidery (like canvas work), but a style of free embroidery.
Crewel yarn is a 2-ply yarn, usually wool, that is chiefly used for crewelembroidery, from which it gets its name, and needlepoint.
Crewelembroidery and needlepoint with crewel yarn are used for pillows and chair seats, for curtains and wall hangings, and for ornamenting clothing and other items.
In crewelembroidery, a design is transferred to a base fabric, and then worked with crewel yarn using suggested stitches from the crewelembroidery repertoire.