The story
The earliest usage is thought to be that of English mathematician William Burnside in 1911, W. Burnside, Theory of Groups of Finite Order, 2nd Edition, in a comment about the Mathieu groups.
Etymology from Wiktionary, CC BY-SA 4.0.
sporadic group
Today it means: Any one of the 26 exceptional finite simple groups, which do not belong to any of the general, infinite categories specified by the classification theorem for finite simple groups. Full definition →