Jacket fastener (4)
I believe the answer is:
snap
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">jacket fastener</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for snap that I've seen before include "Break - children's card game" , "Crack; bite" , "Card game for children" , "Sudden break" , "Picture" .)