Yellow — bird (7)
I believe this clue is a double definition.
'yellow' is the first definition.
(as in cowardly)
'bird' is the second definition.
(I know that chicken is a type of domesticated bird)
(Other definitions for chicken that I've seen before include "Meat" , "Prov. cowardly bird" , "Informally cowardly like domestic fowl" , "Pigeon-hearted" , "Cowardly (colloq.)" .)
'yellow bird' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for canary that I've seen before include "This flies" , "Yellow singing bird" , "Songbird once used to detect toxic gases in mines" , "Bright yellow shade" , "A yellow singing cage-bird" .)