1. fat cell-cells composed of fat. adipose cell. somatic cell, vegetative cell-any of the cells of a plant or animal except the reproductive cells; a cell that does not participate in the production of gametes; somatic cells are produced from preexisting cells;. fat cell-cells composed of fat. adipose cell. somatic cell, vegetative cell-any of the cells of a plant or animal except the reproductive cells; a cell that does not participate in the production of gametes; somatic cells are produced from preexisting cells;