Synonyms for Moonfish (same or very similar meaning)
WordNet sense 1 (any of several silvery marine fishes with very flat bodies):
dollarfish, horsefish, horsehead, horse-head, Atlantic moonfish, Selene setapinnisWordNet sense 2 (large elliptical brightly colored deep-sea fish of Atlantic and Pacific and Mediterranean):
opah, Lampris regiusFrom the ODE community, based on WordNetadd/edit