Open English Wordnet
Nouns
(n)speculation, conjecturea hypothesis that has been formed by speculating or conjecturing (usually with little hard evidence)“speculations about the outcome of the election”, “he dismissed it as mere conjecture”
(n)guess, conjecture, supposition, surmise, surmisal, speculation, hypothesisa message expressing an opinion based on incomplete evidence
Verbs
(v)speculate, theorize, theorise, conjecture, hypothesize, hypothesise, hypothecate, supposeto believe especially on uncertain or tentative grounds“Scientists supposed that large dinosaurs lived in swamps”