Light aquatic bird following short path (7)
I believe the answer is:
lantern
'light' is the definition.
(lantern is a type of light)
'aquatic bird following short path' is the wordplay.
'aquatic bird' becomes 'tern' (tern is a kind of aquatic bird).
'following' says to put letters next to each other.
'short' means to remove the last letter.
'path' becomes 'lane' (lane is a kind of path).
'lane' with its final letter taken off is 'lan'.
'tern' after 'lan' is 'LANTERN'.
(Other definitions for lantern that I've seen before include "Type of lamp" , "Light in a transparent protective case" , "Encased light" , "Light in a protective casing" , "Light held by 26/27 Across" .)