Conjecture, hypothesis (6)
I believe the answer is:
theory
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">conjecture</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">hypothesis</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that hypothesis can be written as theory)</span><br/ ><br/ ></span>
(Other definitions for theory that I've seen before include "Set of ideas formulated to explain something" , "Unproven explanation" , "abstract reasoning" , "Idea formulated to explain something" , "Hypothesis or concept" .)