hypothesis in WordNet English dictionary

1. a message expressing an opinion based on incomplete evidence
   guess  conjecture  supposition  surmise  surmisal  speculation  hypothesis 
   
2. a tentative insight into the natural world; a concept that is not yet verified but that if true would explain certain facts or phenomena
   "a scientific hypothesis that survives experimental testing becomes a scientific theory"; "he proposed a fresh theory of alkalis that later was accepted in chemical practices"
   hypothesis  possibility  theory 
   
3. a proposal intended to explain certain facts or observations
   hypothesis