The Collaborative International Dictionary of English v.0.48:
Sunfish \Sun"fish`\, n. (Zool.)
(a) A very large oceanic plectognath fish (Mola mola, Mola
rotunda, or Orthagoriscus mola) having a broad body
and a truncated tail.
(b) Any one of numerous species of perch-like North American
fresh-water fishes of the family Centrachidae. They
have a broad, compressed body, and strong dorsal spines.
Among the common species of the Eastern United States are
Lepomis gibbosus (called also bream, pondfish,
pumpkin seed, and sunny), the blue sunfish, or
dollardee (Lepomis pallidus), and the long-eared
sunfish (Lepomis auritus). Several of the species are
called also pondfish.
(c) The moonfish, or bluntnosed shiner.
(d) The opah.
(e) The basking, or liver, shark.
(f) Any large jellyfish.