Cousin of a bittern (5)
I believe the answer is:
egret
'cousin of a bittern' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for egret that I've seen before include "Wading bird like a heron" , "Stork-like bird" , "Kind of white heron - greet it" , "Wader with white plumage" , "White, plumed waterbird" .)