Burden powerless tradesman (6)

I believe the answer is:
lumber
This clue could be a double definition.
'burden' is the first definition.
(thesaurus)
'powerless tradesman' is the second definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
Can you help me to learn more?
(Other definitions for lumber that I've seen before include "Cut timber - useless objects" , "Move awkwardly - unwanted household items" , "Move clumsily - Jack's wood?" , "articles in storage" , "With difficulty move" .)
