Put six feet under with sick note by doctor (6)
I believe the answer is:
entomb
'put' is the definition.
(thesaurus)
'sick note by doctor' is the wordplay.
'sick' indicates anagramming the letters.
'by' says to put letters next to each other.
'doctor' becomes 'mb' (Bachelor of Medicine, Medicinae Baccalaureus).
'note' anagrammed gives 'ento'.
'ento'+'mb'='ENTOMB'
'six feet under with' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for entomb that I've seen before include "Place in a sepulchre" , "shut up patients?" , "put away body" , "Incarcerate" , "to finish Aida, for example" .)