Fear terrible pain, chicken-hearted (5)
I believe the answer is:
panic
'fear' is the definition.
(I know that panic is a type of fear)
'terrible pain chicken-hearted' is the wordplay.
'terrible' indicates anagramming the letters.
'hearted' says to take the centre.
The middle letter of 'chicken' is 'c'.
'pain' anagrammed gives 'pani'.
'pani'+'c'='PANIC'
(Other definitions for panic that I've seen before include "much unease" , "Extreme fear" , "Fearful confusion" , "Sudden uncontrollable fear" , "Blind fear" .)