Rigid social stratum (5)
I believe the answer is:
caste
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">rigid social stratum</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for caste that I've seen before include "Social position" , "Hindu determinant of status" , "Level in society" , "Brahmans for instance" , "Division of Hindu society" .)