means Any of a class of greasy, water-repelling organic molecules — fats, oils, waxes, and certain components of cell membranes — that store energy and form the boundaries of every living cell.

from From Greek 'lipos,' meaning fat or grease — the same root behind 'liposuction' and 'lipstick' (literally the waxy stick). The '-id' is the chemist's tidy suffix for a class of compound. The term was coined in the early 20th century as biochemists sorted the body's fatty substances into families, lifting an ancient Greek word for cooking grease into the lab.