The Collaborative International Dictionary of English v.0.48:

Adiaphoristic \Ad`i*aph`o*ris"tic\
   ([a^]d`[i^]*[a^]f`[-o]*r[i^]s"t[i^]k), a.
   Pertaining to matters indifferent in faith and practice.
   --Shipley.
   [1913 Webster]