Short letter (4)
I believe the answer is:
note
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">short letter</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for note that I've seen before include "A, B, C, D, F or G" , "Put down" , "Bill" , "Brief letter - distinction" , "Pay attention to, tone" .)