It's high on the list of headgear (6)
I believe the answer is:
topper
'headgear' is the definition.
(topper is a kind of headgear)
'it's high on the list of' is the wordplay.
'it's high' becomes 'top' (associated in meaning).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'the list of' becomes 'per' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'top'+'per'='TOPPER'
Can you help me to learn more?
(Other definitions for topper that I've seen before include "lid" , "good sort" , "Formal headgear" , "Type of hat (informal)" , "Top hat (colloq.)" .)
