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A mythical creature like a unicorn, however, a tuna fish with a spherical horn upon his head. Often violent and very territorial, extremely dangerous. Reclusive but will attack if it feels threatened.
Marty: I went swimming in the lake yesterday Sarah…the damndest thing happened…
Sarah: What my love?
Marty: I felt this poking in my butthole and when I waded out of the water to investigate, I found, much to my dismay, a fuckin’ goldfish with a horn stickin’ out of my ass!
Sarah: Oh my God! You were cornholed by a tunacorn!!!!!
by donkey shave August 28, 2009
A tuna with a unicorn's horn. Often described to make the sound, "mwow."
"MWOW!" said the tunacorn.
by TEH First Tunacorn October 03, 2005