Old tree likely to get hollowed out (7)
I believe the answer is:
elderly
'old' is the definition.
(elderly means old or aged)
'tree likely to get hollowed out' is the wordplay.
I cannot really see how this works, but
'tree' could be 'elder' (elder is a kind of tree) and 'elder' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for elderly that I've seen before include "over the hill" , "Fairly old, past middle age" , "Mature" , "Silver" , "... or not of tender years" .)