Irrational belief (12)
I believe the answer is:
superstition
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">irrational belief</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for superstition that I've seen before include "Credulous belief" , "Irrational belief in the supernatural" .)