The Collaborative International Dictionary of English v.0.48:

BC \BC\, B C \B. C.\n.
   before Christ; used in reckoning dates before the supposed
   year Christ was born, i.e. 1 a. d..
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

BC
    adv 1: before the Christian era; used following dates before the
           supposed year Christ was born; "in 200 BC" [syn: BC,
           B.C., before Christ]

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

BC

   An arbitrary precision numeric processing language with
   C-like syntax.  Traditionally implemented as a front-end
   to DC.  There is a GNU version called GNU BC.

   Unix manual page: bc(1).