Pre-migraine phenomenon for some (4)
I believe the answer is:
aura
'pre-migraine phenomenon for some' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for aura that I've seen before include "Distinctive quality (of something or someone)" , "Emanation - distinctive air" , "Atmosphere, quality" , "Characteristic air of person" , "Indiscernible quality" .)