Flagellate and Protozoan

Flagellate noun - A usually nonphotosynthetic free-living protozoan with whiplike appendages; some are pathogens of humans and other animals.

Protozoan and flagellate are semantically related In some cases you can use "Protozoan" instead a noun "Flagellate".

Protozoan noun - Any of diverse minute acellular or unicellular organisms usually nonphotosynthetic.

Flagellate and protozoan are semantically related in minute organism topic. You can use "Flagellate" instead a noun "Protozoan".