A religion (5)
I believe the answer is:
islam
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">a religion</span>' is the definition.<br/ ><span class="explanation-format__explanation">(Islam is a religion)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for islam that I've seen before include "Mails to Muslim religion" , "Adherents of a religion" , "Belief" , "Mails to great eastern religion" , "Koran its scripture" .)