A single organism is a living being that is made up of one cell. The term AMOEBA (6 letters) is used to describe a type of single-celled organism that can change its shape and move around. MONAD (5 letters) is another term for a single-celled organism, which is also known as a unicellular organism. Aerobe (6 letters) is a type of single-celled organism that requires oxygen to survive. Ameba (5 letters) is another name for an AMOEBA. All of these terms refer to a single organism, which is a living being made up of one cell.