eosinophil A type of white blood cell (leucocyte) that has a granular cytoplasm (see granulocyte). Its function involves the regulation of allergic responses and it also produces an enzyme capable of destroying parasites.

eosinophil (ee-oh-sin-ŏ-fil) n. a variety of white blood cell (see polymorph) distinguished by the presence in its cytoplasm of coarse granules that stain orange-red with Romanowsky stains. Eosinophils are capable of ingesting foreign particles and are involved in allergic responses and host defence against parasites.