Chirrup; message (5)
I believe the answer is:
tweet
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">chirrup</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that chirrup can be written as tweet)</span><br/ ><br/ >'<span class="explanation-format__original">message</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(type of online message)</span><br/ ><br/ ></span>
(Other definitions for tweet that I've seen before include "Message of up to 140 characters" , "online comment" , "Message from Trump?" , "(Make a) chirping noise" , "Twitter" .)