Nautical drink
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">nautical drink</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for grog that I've seen before include "Naval rum issue" , "Rum mixed with water" , "Sailors' drink of rum and water" , "Rum cut with water" , "Old naval drink" .)