Step 1: To \textit{hypothesize} means to suggest or assume an explanation or theory that can be tested or debated. It involves proposing an idea that might explain certain facts.
Step 2: The opposite of hypothesizing would be to reject or disprove a proposed theory. This is expressed by the word \textit{refute}, which means to prove a hypothesis or statement to be false or incorrect.
Step 3: Options (A) posit, (B) propose, (C) conjecture, and (E) speculate are all synonyms or near-synonyms of hypothesize, since they all involve suggesting ideas.
Step 4: Only (D) refute provides the opposite meaning, as it negates or disproves a hypothesis.