Short period of calm (4)
I believe the answer is:
lull
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">short period of calm</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 lull that I've seen before include "A temporary period of quiet, as in storm" , "Calm interval in storm" , "Put to sleep - respite" , "Short period of quiet" , "Cessation of activity (before a storm?)" .)