Discharge letter by medical department following illness (8)
I believe the answer is:
effluent
'discharge' is the definition.
(thesaurus)
'letter by medical department following illness' is the wordplay.
'letter' becomes 'eff' (name for the letter F).
'by' says to put letters next to each other.
'medical department' becomes 'ENT' (abbreviation for Ear, Nose and Throat department).
'following illness' becomes 'lu' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'ent' after 'lu' is 'luent'.
'eff'+'luent'='EFFLUENT'
Can you help me to learn more?
(Other definitions for effluent that I've seen before include "contents of 25 [SEWER]" , "sewage" , "Sewer water" , "Outflow of liquid waste matter" , "Waste water" .)