parasite

noun

Sam was a parasite with no interest in anything but drink and gambling:

hanger-on, leech, passenger, drone;

informal bloodsucker, sponger, sponge, scrounger, freeloader;

British, informal ligger, cadger;

North American, informal moocher, mooch;

Australian, New Zealand, informal bludger.

word links	parasite
parasitophobia fear of parasites parasitology branch of medicine concerning parasitic organisms

parasite Oxford Dictionary of English