Lipids: Another word for "fats." (Please see the various meanings of Fat.) Lipids can be more formally defined as substances such as a fat, oil or wax that dissolves in alcohol but not in water. Lipids contain carbon, hydrogen and oxygen but have far less oxygen proportionally than carbohydrates.
Lipids are an important part of living cells. Together with carbohydrates and proteins, lipids are the main constituents of plant and animal cells.
Lipids include fatty acids, neutral fats, waxes and steroids (like cortisone). Compound lipids (lipids complexed with another type of chemical compound) comprise the lipoproteins, glycolipids and phospholipids.
Etymology: Whereas the everyday term "fat" comes from the Old English (from "faett" meaning crammed or adorned), the more scientific term "lipid" comes from the Greek "lipos" which referred to animal fat or vegetable oil.