Type of light lake punt associated with Royal Navy (7)
I believe the answer is:
lantern
'type of light' is the definition.
'lake punt associated with royal navy' is the wordplay.
'lake' becomes 'l'.
'punt' becomes 'ante' (anteing is a kind of punting).
'associated with' is a charade indicator (letters next to each other).
'royal navy' becomes 'rn'.
'l'+'ante'+'rn'='LANTERN'
(Other definitions for lantern that I've seen before include "Leading light" , "Portable light source" , "Transparent case for holding a light" , "Light in a transparent protective case" , "Enclosed light" .)