Tree found in Arundel mainly (3)
I believe the answer is:
elm
'tree' is the definition.
(elm tree is a kind of tree)
'in arundel mainly' is the wordplay.
'in' indicates a hidden word.
'ELM' is hidden in the letters of 'arundel mainly'.
'found' acts as a link.
(Other definitions for elm that I've seen before include "Gray's rugged tree (Elegy)" , "Tough timber" , "Tree for a Cockney tiller" , "Large tree" , "one has a trunk and leaves" .)