Oil that is obtained from walnuts that are pressed to extract the natural oil. The richly flavored oil makes it a good choice for use in salad dressings and sauces, but it is more expensive than several other popular oils such as corn oil or canola oil. It is best to store it in the refrigerator to prevent it from becoming rancid. If refrigeration causes the oil to solidify, it can be restored to a liquid state by leaving it at room temperature for an hour or two. Like other oils obtained from nuts, walnut oil is very popular in French cooking.