Fair distance not half negotiated for medical treatment (5,3)
I believe the answer is:
first aid
'medical treatment' is the definition.
(I've seen this before)
'fair distance not half negotiated' is the wordplay.
'not half' means to take half the letters.
'negotiated' indicates an anagram.
'distance' halved is 'dist'.
'fair'+'dist'='fairdist'
'fairdist' is an anagram of 'FIRST-AID'.
'for' is the link.
(Other definitions for first aid that I've seen before include "Immediate medical help pending full treatment" , "Basic medical help" , "Immediate medical assistance" , "Emergency medical treatment" , "'Immediate emergency care (5,3)'" .)