Certain service
I believe the answer is:
mass
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">certain service</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 mass that I've seen before include "Substance; a service" , "Religious celebration" , "13 [BULK]" , "Quantity; religious service" , "Church rite; large group" .)