Rant about the medical possibility (7)
I believe the answer is:
declaim
'rant' is the definition.
(I've seen this before)
'the medical possibility' is the wordplay.
'possibility' indicates anagramming the letters (another possible arrangement of the letters).
'medical' with letters rearranged gives 'DECLAIM'.
'about' acts as a link.
(Other definitions for declaim that I've seen before include "Hold forth" , "Deliver (words) rhetorically" , "Harangue" , "Utter rhetorically" , "Deliver (words) impressively" .)