Submarine (8)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">submarine</span>' is the definition.<br/ ><span class="explanation-format__explanation">(submarine means under the sea)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for undersea that I've seen before include "Below marine surface" , "Beneath the oceans" , "submerged" , "Submarine" , "Where bed is" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">submarine</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that submarine can be written as U-boat)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for u-boat that I've seen before include "Take pool exercise" , "German World War One or World War Two submarine" , "Sea vessel" , "Submersible warship of WWII" , "German WW 2 sub" .)