Hard wood to control (4)
I believe the answer is:
helm
'control' is the definition.
(thesaurus)
'hard wood' is the wordplay.
'hard' becomes 'h'.
'wood' becomes 'elm' (elm is a kind of wood**).
'h'+'elm'='HELM'
'to' is the link.
(Other definitions for helm that I've seen before include "Steering gear" , "Position of leadership" , "Wheel that controls ship's rudder" , "Steersman's place" , "Steering device" .)