Height above sea level (8)
I believe the answer is:
altitude
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">height above sea level</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for altitude that I've seen before include "Height above sea-level" , "Height, elevation" , "Lofty position" , "high place" , "Elevation above sea level" .)