pro ‧ to ‧ zo ‧ an /ˌprəʊtəˈzəʊən $ ˌproʊtəˈzoʊən/ BrE AmE ( also pro‧to‧zo‧on /-ˈzəʊɒn $ -ˈzoʊɑːn/) noun ( plural protozoa /-ˈzəʊə $ -ˈzoʊə/ or protozoans ) [countable]
[ Date: 1800-1900 ; Language: Modern Latin ; Origin: Greek , 'first animal' ]
a very small living thing that has only one cell
—protozoan adjective