Adage, dictum (5)
I believe the answer is:
maxim
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">adage</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >'<span class="explanation-format__original">dictum</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ ></span>
(Other definitions for maxim that I've seen before include "Old machine-gun" , "Short pithy statement" , "Axiom" , "Apophthegm" , "Principle-first machine gun" .)