parasite

noun parasites

1. An organism that lives on or in another organism of a different species, deriving benefit from living on or in that other organism, while not contributing towards that other organism sufficiently to cover the cost to that other organism. Lice, fleas, ticks, and mites are widely spread parasites.
2. informal, specifically An internal parasite that is an animal or protist. He lacks, however, even the basic Dr. Kildare lingo about medical issues. For instance, he regularly misidentifies poppers as amyl nitrate, instead of amyl nitrite — two forms of heart medicine with different affects ^([sic]). Salmonella, a bacteria, is not usually classified as a parasite. And he m
3. derogatory A person who lives on other people's efforts or expense and gives little or nothing back. Of all the corrupting effects of wealth there is none worse than this, that it makes the wealthy (and their parasites) think in some way divine, or at least a lovely character of the mind, what is in truth nothing but their power of luxurious living.

   Similar: bloodsucker, bludger, bummer, freeloader, free rider, gadfly, leech, mooch, moocher, parasite, scrounge, scrounger

4. derogatory A sycophant or hanger-on.
5. literary, poetic A climbing plant which is supported by a wall, trellis etc. Her golden tresses shade / The bosom's stainless pride, / Curling like tendrils of the parasite / Around a marble column.
6. historical A retainer or companion of an ancient Celtic warrior, who praised him in song or poetry at gatherings; a bard.
7. A component of a composite aircraft which is carried aloft and air-launched by a larger carrier aircraft or mother ship to support the primary mission of the carrier; a parasite aircraft. […] parasiting and aerial refueling as range-extension measures. Second, parasiting would be exorbitantly expensive, because each parasite bomber would need its own carrier. Two bombers could be serviced by a single tanker, however,[…]
8. attributive An isolated (FSDU) (freestanding display unit ) parasite display

Opposite: commensal, mutualist, sometimes symbiote

verb parasites · parasiting · parasited

1. rare To parasitize. ... parasiting upon her husband, taking everything and giving nothing in return, this woman had brought her husband to a condition of serious ill health because of his grief, anxiety, and despair over her failure.