Biology. An organism that lives on, in, or with an organism of another species, obtaining food, shelter, or other benefit; (now) spec. one that…

Pathology. A vegetable parasite on the surface of an animal body.

a facultative parasite, e.g. certain fungi; also a plant which is partially parasitic, drawing water and mineral nutrients but not synthesized foods…

(see quot.).

A parasite, esp. a fungus, that derives nutrition from living cells of a host plant.