Enrolment (12)
I believe the answer is:
registration
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">enrolment</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for registration that I've seen before include "Vehicle identifier" , "Car ID" , "signing up" , "Car identifier" , "Formal enrolment" .)