Grieve over (5)
I believe the answer is:
mourn
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">grieve over</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 mourn that I've seen before include "Weep for" , "Show sorrow at death" , "'Miss'" , "Express sadness" , "Regret (a loss)" .)