A person with an unusual or odd personality; an eccentric person. (informal)
Synonyms:eccentric, eccentric person, geek.
2.
Hence: Anything unusual in its class. "Pluto is an oddball among its eight sister planets. It's the smallest in both size and mass, and has the most elliptical orbit. It moves in a plane tilted markedly away from the other planets' orbits. Moreover, Pluto is the only planet made almost entirely of ice."
adjective
oddball adj. Eccentric; very unusual; strange; bizarre; as, an oddball request. (informal)
... issue. As for that, I don't know any more than you do. There's never been anything like this. Colonists have been wiped out on other planets, sure; but what happened left traces. This one is an oddball, and I'd say you're as well equipped to handle ... — Eight Keys to Eden • Mark Irvin Clifton