Highway heavyweight (4)
I believe the answer is:
semi
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">highway heavyweight</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for semi that I've seen before include "Dwelling" , "Prefix denoting half" , "Co-joined house" , "Prefix meaning half (4)" , "Residence" .)