means A person, thing, or quirk that stands out as strange, unusual, or hard to categorize.

from From 'odd' plus the noun-forming suffix '-ity.' 'Odd' itself came into English from Old Norse 'oddi,' which meant a point or triangle of land — and, by extension, the odd one left over when things are paired off, the unmatched third. So an oddity is, at its root, the leftover that didn't fit the pattern.