Keep a check on (7)
I believe the answer is:
monitor
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">keep a check on</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for monitor that I've seen before include "what a computer user may require" , "Security camera" , "Keep track of" , "Checking device - VDU - lizard" , "School pupil assigned responsibilities" .)