The term 'single-celled animal' can be summarized by the crossword solution 'AMOEBA' (6 letters). Amoebas are single-celled organisms that belong to the kingdom Protista. They are classified as eukaryotes, meaning they have a nucleus and other organelles enclosed within a membrane. Amoebas are found in a variety of habitats, including freshwater, soil, and marine environments. They feed on bacteria and other small organisms, and reproduce asexually by dividing into two daughter cells.