The Collaborative International Dictionary of English v.0.48:

Perissad \Per"is*sad\, a. [Gr. ? odd, from ? over.] (Chem.)
   Odd; not even; -- said of elementary substances and of
   radicals whose valence is not divisible by two without a
   remainder. Contrasted with artiad. [Archaic]
   [1913 Webster]