Discharge sailor in arch ploy (7)
I believe the answer is:
catarrh
'discharge' is the definition.
(discharge in the nose or throat)
'sailor in arch ploy' is the wordplay.
'sailor' becomes 'tar' (term for a sailor).
'in' means one lot of letters goes inside another.
'ploy' indicates an anagram (ploy can mean a trick or scheme).
'arch' is an anagram of 'carh'.
'tar' going inside 'carh' is 'CATARRH'.
(Other definitions for catarrh that I've seen before include "Head cold" , "Nasal problem" , "Arch rat with inflamed mucous membrane" , "cold symptom" , "Nasal congestion" .)