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

cross-assembler

   An assembler which runs on one type of processor and
   produces machine code for another.

   There is a set of 6502, 68xx and Zilog Z80 and 8085
   cross-assemblers in C by  and Alan
   R. Baldwin.  They run under MS-DOS and could be compiled to
   run under Unix and on the Amiga and Atari ST.

   See also fas.

   (ftp://ccosun.caltech.edu/).

   (1993-03-10)