Definition of superstock in US English:

superstock

noun

  • 1Originally and chiefly US. An (extensively) modified car, motorcycle, or other vehicle; specifically (in later use) a stock car in a racing class subject to fewer restrictions regarding modification than normal stock cars; the class to which such vehicles belong. Compare "stock".

  • 2Linguistics. A group of language families believed to have developed from a single common ancestor.

Origin

Late 19th century (in an earlier sense). From super- + stock.