The Collaborative International Dictionary of English v.0.48:

Adiaphorist \Ad`i*aph"o*rist\ ([a^]d`[i^]*[a^]f"[-o]*r[i^]st),
   n. [See Adiaphorous.] (Eccl. Hist.)
   One of the German Protestants who, with Melanchthon, held
   some opinions and ceremonies to be indifferent or
   nonessential, which Luther condemned as sinful or heretical.
   --Murdock.
   [1913 Webster]