Fir or poplar (4)
I believe the answer is:
tree
This clue is a double definition.
'fir' is the first definition.
(thesaurus)
'poplar' is the second definition.
(I've seen this in another clue)
(Other definitions for tree that I've seen before include "May" , "Eg, laburnum" , "eg Lime" , "Be up a .... to be in difficulties" , "Shoe stretcher" .)