A primitive life form is an organism that has not evolved much over time. The term 'primitive life form' is often used to refer to single-celled organisms, such as the AMOEBA, which is a 6-letter word in this crossword puzzle. Amoebas are unicellular organisms that lack a true nucleus and reproduce by cell division. They are found in a variety of environments, from freshwater to soil, and can survive in extreme conditions.