Second method to gain supremacy (4)
I believe the answer is:
sway
'supremacy' is the definition.
(thesaurus)
'second method' is the wordplay.
'second' becomes 's' (common abbreviation).
'method' becomes 'way' (I've seen this before**).
's'+'way'='SWAY'
'to gain' acts as a link.
(Other definitions for sway that I've seen before include "Move from side to side; influence" , "Pitch sideways" , "Move gently" , "Bend; influence" , "Oscillate" .)