The old man needs shelter, that's clear (6)
I believe the answer is:
patent
'clear' is the definition.
('patent' can be a synonym of 'clear')
'the old man needs shelter' is the wordplay.
'the old man' becomes 'pa' ('pa' can be a synonym of 'old man').
'needs' says to put letters next to each other.
'shelter' becomes 'tent' (tent is a kind of shelter).
'pa'+'tent'='PATENT'
'that's' is the link.
(Other definitions for patent that I've seen before include "It's registered to protect an invention" , "Document granting an inventor sole rights to an invention" , "For all to see" , "Manifest" , "Flagrant" .)