The Collaborative International Dictionary of English v.0.48:

Dyadic \Dy*ad"ic\, a. [Gr. ?, fr. ? two.]
   Pertaining to the number two; of two parts or elements.
   [1913 Webster]

   Dyadic arithmetic, the same as binary arithmetic.
      [1913 Webster]

WordNet (r) 3.0 (2006):

dyadic
    adj 1: of or relating to a dyad or based on two

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

dyadic

    binary (describing an operator).

   Compare monadic.

   (1998-07-24)