Vast body of water (5)
I believe the answer is:
ocean
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">vast body of water</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ocean that I've seen before include "Large body of salt water" , "An immense expanse of sea" , "Huge body of water" , "eg Indian, Atlantic" , "Quantity of water" .)