Grounds, for instance, accepted by doctors (5)
I believe the answer is:
dregs
'grounds' is the definition.
(synonyms)
'for instance accepted by doctors' is the wordplay.
'for instance' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'accepted by' means one lot of letters goes inside another (inserted letters are accepted).
'doctors' becomes 'Drs' ('Dr' can be a synonym of 'doctor').
'eg' put into 'drs' is 'DREGS'.
(Other definitions for dregs that I've seen before include "Sediment at the bottom of a liquid" , "Fluid remnants" , "Parts of least value" , "Most worthless part (of anything)" , "Sediment at bottom of drink" .)