WordNet (r) 3.0 (2006):

xc
    adj 1: being ten more than eighty [syn: ninety, 90, xc]
    n 1: the cardinal number that is the product of ten and nine
         [syn: ninety, 90, XC]

V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

XC
       eXtended Configuration (IBM, ESA, VM)


The Free On-line Dictionary of Computing (30 December 2018):

XC

   A declarative extension of C++.

   ["XC - A Language for Embedded Rule Based Systems", E. Nuutila
   et al, SIGPLAN Notices 22(9):23-32 (Sep 1987)].