Irregular; not smooth (5)
I believe the answer is:
rough
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">irregular</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(associated in meaning)</span><br/ ><br/ >'<span class="explanation-format__original">not smooth</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know this)</span><br/ ><br/ ></span>
(Other definitions for rough that I've seen before include "Uneven, harsh" , "Rasping" , "Approximate; hooligan" , "Approximate; turbulent" , "Drivers try to steer clear of this" .)