Knot on a tree trunk (5)
I believe the answer is:
gnarl
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">knot on a tree trunk</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 gnarl that I've seen before include "lump of wood" , "Rough lump (on a tree)" , "Tree-swelling" , "Lump, growl" , "Something lumpy" .)