Start to smoke (5,2)
I believe the answer is:
light up
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">start to smoke</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for light up that I've seen before include "what floods can do" , "Ignite a cigarette; suddenly show joy" , "as one may with a cigarette" , "Start dragging in" , "Start smoking" .)