Begin to understand (6,2)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">begin to understand</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 cotton on that I've seen before include "Downy fibre attached to" , "Come to understand" , "Get wise (to)" , "Understand (slang)" , "what a cool dresser has, perhaps" .)