Unauthorised absence from school (7)
I believe the answer is:
truancy
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">unauthorised absence from school</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 truancy that I've seen before include "bunking off" , "Unauthorised absence from school" , "Failure to attend school" , "Staying away from school" .)