The Collaborative International Dictionary of English v.0.48:

Myronic \My*ron"ic\, a. [Gr. my`ron a sweet-smelling unguent.]
   (Chem.)
   Pertaining to, or obtained from, mustard; -- used
   specifically to designate a glucoside called myronic acid,
   found in mustard seed.
   [1913 Webster]