Large tree branch (4)
'large tree branch' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for limb that I've seen before include "Human's extension" , "Bough" , "Branch - arm - leg" , "Wing, perhaps" , "Branch of a tree (risky to go out on)" .)
(Other definitions for bough that I've seen before include "Substantial branch of a tree" , "Main branch (of tree)" .)