Physics quantity (4)
I believe the answer is:
mass
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">physics quantity</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 "Body of matter" , "Accumulation" , "Rite; quantity of matter" , "congregation for > service" , "Roman Catholic service" .)