The American Heritage® Dictionary of the English Language, 4th Edition
n. A calorie-free fat substitute synthesized from sucrose and vegetable oil for use in snacks such as potato chips, and capable of passing through the body without being digested.
n. A fat substitute (a glyceride of sucrose) that cannot be easily digested and therefore adds no fat, calories, or cholesterol to food products; also used as an industrial lubricant.
Word Usage
"A product called olestra has been approved by health authorities in the United States for sale."