1) Anticipate 2) Believe on uncertain grounds 3) Conceive 4) Conjecture 5) Expect 6) Hypothecate 7) Hypothesise 8) Imagine 9) Make a tentative assumption 10) Posit 11) Put forward 12) Speculate 13) Suppose 14) Theorise 15) Theorize 1) Assume 2) Formulate 3) Guess 4) Hypothesise 5) Opine 6) Posit 7) Reconstruct 8) Speculate 9) Theorise 10) Theorize 11) Wonder 
to make an educated guess (a hypothesis) based on observations; in science, hypothesizing is often followed by experimenting in order to try to prove the hypothesis
hypothesize 1. To theorize, speculate, guess, suppose, and to presume. 2. To give a possible but not yet proved explanation for something