Underpass (6)
I believe the answer is:
subway
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">underpass</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that underpass can be written as subway)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for subway that I've seen before include "Underground rail" , "pedestrian passage?" , "American tube" , "US underground railway" , "Passage under a road" .)