Rain heavily; abound (4)
I believe the answer is:
teem
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">rain heavily</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >'<span class="explanation-format__original">abound</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 "Abound, swarm with" , "Rain buckets" , "Move in large numbers" , "Abound - pour" , "(Of rain) fall heavily" .)