Tiller doesn't use hard wood (3)
I believe the answer is:
elm
'wood' is the definition.
(elm is a type of tree)
'tiller doesn't use hard' is the wordplay.
'tiller' becomes 'helm' (I've seen this before).
'doesn't use' indicates named letters should be taken away.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'helm' with 'h' removed is 'ELM'.
(Other definitions for elm that I've seen before include "Furniture wood" , "Large tree" , "Tree of the genus Ulmus" , "Stately tree" , "Leaving body" .)