Sound the horn (4)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sound the horn</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for honk that I've seen before include "Toot one's horn" , "Cry of the wild goose" , "Cry of a goose - sound of a horn" , "Toot of a horn - cry of a goose - smell nasty" .)