Invade in great numbers (7)
I believe the answer is:
overrun
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">invade in great numbers</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for overrun that I've seen before include "Go on too long (of a performance)" , "Infest; carry beyond the limit" , "Exceed (allowed cost/time)" , "Exceed time allowed, or spread across and injure (7)" , "Swarm over" .)