The term UNIT OF LIFE can be solved by the crossword solution CELL, which is a four letter word. A CELL is the basic unit of life in all living organisms and is the smallest unit of life that can exist independently. Cells are made up of a variety of components, including a nucleus, cytoplasm, and CELL membrane. Cells are responsible for many of the functions of living organisms, such as growth, reproduction, metabolism, and energy production.