cyclops

(noun) (Greek mythology) one of a race of giants having a single eye in the middle of their forehead. Synonyms: Cyclops.

(noun) minute free-swimming freshwater copepod having a large median eye and pear-shaped body and long antennae used in swimming; important in some food chains and as intermediate hosts of parasitic worms that affect man e.g. Guinea worms. Synonyms: water flea.