Echelon (4)
I believe the answer is:
tier
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">echelon</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 tier that I've seen before include "Wedding cake feature" , "One securing" , "range" , "Person joining" , "Rite for a rank" .)