Sufferer's losing heart, it's clear (6)
I believe the answer is:
patent
'clear' is the definition.
('patent' can be a synonym of 'clear')
'sufferer's losing heart' is the wordplay.
'sufferer' becomes 'patient' (patient is a kind of sufferer).
'losing heart' says to hollow out the word (remove centre letters).
'patient' with its middle removed is 'PATENT'.
'it's' acts as a link.
(Other definitions for patent that I've seen before include "It protects an invention" , "Obvious, unconcealed" , "Blatant" , "Licence for inventors; obvious" , "Manifest" .)