Yellow head of crocodile bird (6)
I believe the answer is:
craven
'yellow' is the definition.
(thesaurus)
'head of crocodile bird' is the wordplay.
'head of' says to take the initial letters.
'bird' becomes 'raven' (raven is a kind of bird).
The first letter of 'crocodile' is 'c'.
'c'+'raven'='CRAVEN'
(Other definitions for craven that I've seen before include "Mean-spirited" , "Contemptibly cowardly" , "Chicken" , "Cowardly - Yorkshire area" , "Lacking courage, cowardly" .)