Source : Webster's Revised Unabridged Dictionary (1913)

Episyllogism \Ep`i*syl"lo*gism\, n. [Pref. epi- + syllogism.]
   (Logic)
   A syllogism which assumes as one of its premises a
   proposition which was the conclusion of a preceding
   syllogism, called, in relation to this, the prosyllogism.