Frightened to pay out the old devil! (7)
I believe the answer is:
panicky
'frightened' is the definition.
(I know that frightened can be written as panicky)
'pay out the old devil' is the wordplay.
'out' means one lot of letters goes inside another.
'the old devil' becomes 'nick' (I've seen this before).
'pay' placed around 'nick' is 'PANICKY'.
'to' is the link.
(Other definitions for panicky that I've seen before include "nervous!" , "Very worried" , "Dreadfully anxious" , "Suffering fear, anxiety" , "in a tizzy" .)