Wiktionary
n. A fin located on the backs of fish and some marine mammals.
WordNet
n. unpaired median fin on the backs of fishes and some other aquatic vertebrates that help to maintain balance
Wikipedia
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fish, cetaceans ( whales, dolphins, and porpoises), and the (extinct) ichthyosaurs. Depending on the species, an animal may have one or two of them.
Wildlife biologists often use the distinctive nicks and wear patterns which develop on the dorsal fins of large cetaceans to identify individuals in the field.
The bony or cartilaginous bones that support the base of the dorsal fin in fish are called pterygiophores.
Usage examples of "dorsal fin".
But he caught a dorsal fin as he was tumbled underwater and hung on until he and - it was Cal he’.
Orley grabbed Tsh't's dorsal fin as she was about to whistle the command.
Instantly the dolphin took off, and Nita hoisted herself up to a better position, hanging from the dorsal fin so that her body was half out of the water and her legs were safely out of the way of the fiercely lashing tail.
Tu'uua'col stood not quite six feet tall but seemed much taller due to the dorsal fin that started between his full black eyes and jutted up nearly a foot above his head before running all the way down his back to his buttocks.
They stepped carefully onto its slippery, muddy hide and clambered toward the dorsal fin above.
Another ladulta spiraled by, swimming spasmodically in a jerky spiral, with Saito no longer holding its dorsal fin, but now swimming alongside as if trying to help the creature to the surface.
It had a more aquatic-looking dorsal fin and tail, however, except that the tail was cut out and a tiny figure eight stood in the gap.
He had hit the orca just forward of the dorsal fin with both feet, but they had both immediately slid out from under him on the slick skin of the beast and he had impacted on his hip and side, flipping sideways on the right side of the orca, entering the water with a tremendous splash.
Instantly, a dorsal fin cut the water, zooming toward the flailing swimmer.