Old tree likely hollow (7)
I believe the answer is:
elderly
'old' is the definition.
('elderly' can be similar in meaning to 'old')
'tree likely hollow' is the wordplay.
'tree' becomes 'elder' (elder is a kind of tree**).
'hollow' suggests removing the centre.
'likely' with its centre taken out is 'ly'.
'elder'+'ly'='ELDERLY'
(Other definitions for elderly that I've seen before include "over the hill" , "Mature" , "Old or ageing" , "Rather old" , "Silver" .)