"Message received” (5)
I believe the answer is:
roger
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">message received</span>' is the definition.<br/ ><span class="explanation-format__explanation">(radio communications)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for roger that I've seen before include "that's clear" , "Radio confirmation" , "Jolly man" , "Romeo's predecessor" , "One like de Coverley" .)