Abound, be plentiful (4)
I believe the answer is:
teem
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">abound</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">be plentiful</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ ></span>
(Other definitions for teem that I've seen before include "Bear" , "Come down hard" , "Seethe" , "(Of rain) pour down" , "Abound, swarm with" .)