Shrill trumpet (7)
I believe the answer is:
clarion
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">shrill trumpet</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 clarion that I've seen before include "Loud and clear; shrill war trumpet" , "Kind of trumpet" , "Trumpet (now more likely a newspaper)" , "Medieval brass instrument heard in carol" , "Medieval brass instrument with a clear shrill tone" .)