They may crash and break (5)
I believe the answer is:
waves
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">they may crash and break</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 waves that I've seen before include "Breakers" , "Undulations" , "Undulates" , "Ripples" .)