Dam-builder (6)
I believe the answer is:
beaver
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">dam-builder</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 beaver that I've seen before include "Broad-tailed rodent" , "tree-feller" , "Soft furry rodent" , "Hard worker (could also be eager)" , "Hard-working furry rodent" .)