Sentry (5)
I believe the answer is:
guard
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sentry</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for guard that I've seen before include "state of caution" , "Screw" , "One keeps watch" , "Warden; defend" , "Yeomen" .)