A vast amount (5)
I believe the answer is:
ocean
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">a vast amount</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 "eg Indian, Pacific" , "One of the Seven Seas" , "Large body of salt water" , "A lot of water!" , "Large stretch of sea" .)