Speculate, conjecture (8)
I believe the answer is:
theorise
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">speculate</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >'<span class="explanation-format__original">conjecture</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for theorise that I've seen before include "Think up possible explanations" , "Form view" , "Express ideas" , "Conjecture, hypothesise" , "Speculate by reasoning" .)