Unspecified doctrine (3)
I believe the answer is:
ism
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">unspecified doctrine</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 ism that I've seen before include "form of belief?" , "Belief system" , "Informally, any doctrine or practice" , "Distinctive doctrine or practice" , "Stage performance of singing" .)