Swoop, fall upon (6)
I believe the answer is:
pounce
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">swoop</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that swoop can be written as pounce)</span><br/ ><br/ >'<span class="explanation-format__original">fall upon</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ ></span>
(Other definitions for pounce that I've seen before include "Jump down on suddenly" , "Spring or swoop down on to attack" , "Strike" , "Spring (on prey like a cat)" , "Jump swiftly on, as cat might" .)