The Collaborative International Dictionary of English v.0.48:
Surmisal \Sur*mis"al\ (s[^u]r*m[imac]z"al), n. Surmise. [R.] --Milton. [1913 Webster]WordNet (r) 3.0 (2006):
surmisal n 1: a message expressing an opinion based on incomplete evidence [syn: guess, conjecture, supposition, surmise, surmisal, speculation, hypothesis]