As nouns the difference between protozoan and trichomonad

is that protozoan is (cytology) any of the diverse group of eukaryotes, of the phylum protozoa, that are primarily unicellular, existing singly or aggregating into colonies, are usually nonphotosynthetic, and are often classified further into phyla according to their capacity for and means of motility, as by pseudopods, flagella, or cilia while trichomonad is any of many flagellate protozoans, of the genus trichomonas , most of which are parasitic.

As an adjective protozoan

is of, pertaining to, or characteristic of a protozoan.