The Collaborative International Dictionary of English v.0.48:

Operand \Op"er*and\, n. [From neuter of L. operandus, gerundive
   of operari. See Operate.] (Math.)
   The symbol, quantity, or thing upon which a mathematical
   operation is performed; -- called also faciend.
   [1913 Webster]

WordNet (r) 3.0 (2006):

operand
    n 1: a quantity upon which a mathematical operation is performed

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

operand

    An argument of an operator or of a machine
   language instruction.

   (1995-08-18)