King has advantage, a light anchor (5)
I believe the answer is:
kedge
'a light anchor' is the definition.
(I've seen this before)
'king has advantage' is the wordplay.
'king' becomes 'K' (chess abbreviation).
'has' means one lot of letters go next to another.
'advantage' becomes 'edge' (having the edge is having an advantage).
'k'+'edge'='KEDGE'
(Other definitions for kedge that I've seen before include "Use hawser" , "Light anchor" , "Lively" , "Move boat" , "Small anchor" .)