Tree, old, associated with a King (3)
I believe the answer is:
oak
'tree' is the definition.
(oak is a kind of tree)
'old associated with a king' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'associated with' is a charade indicator (letters next to each other).
'king' becomes 'k' (**).
'o'+'a'+'k'='OAK'
(Other definitions for oak that I've seen before include "Acorn-bearing tree" , "Grown acorn" , "Acorn tree" , "The mighty tree" , "Hard durable wood of a deciduous tree" .)