George fire doctor in sadness (5)
I believe the answer is:
grief
'sadness' is the definition.
(I know that grief is a type of sorrow)
'george fire doctor in' is the wordplay.
'george' becomes 'g' ().
'doctor' indicates an anagram.
'in' means one lot of letters goes inside another.
'fire' anagrammed gives 'rief'.
'g' inserted inside 'rief' is 'GRIEF'.
(Other definitions for grief that I've seen before include "Deep sorrow" , "sad state" , "Suffering" , "Heartbreak" , "Deep sadness" .)