Particularly the highest (5,3)
I believe the answer is:
above all
'particularly' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for above all that I've seen before include "Like the managing director" , "Notably" , "Mainly" , "What 18 [EVEREST] is" , "Shakespeare: 'This . . . . . . . ., to thine own self be true'" .)