WordWeb Online

1. Infer from incomplete evidence
    
2. Imagine to be the case or true or probable
   "I surmised that the butler did it"
   - suspect

1. A message expressing an opinion based on incomplete evidence
   - guess, conjecture, supposition, surmisal, speculation, hypothesis

Derived forms: surmising, surmises, surmised

Type of: deduce, deduct, derive, guess, hazard, infer, opinion, pretend, venture, view