Vengeful spirits certainly associated with Hibernia (7)
I believe the answer is:
erinyes
'vengeful spirits' is the definition.
The definition suggests a plural noun which matches the answer.
'certainly associated with hibernia' is the wordplay.
'certainly' becomes 'yes' (both can be used to answer in the affirmative).
'associated with' is a charade indicator (letters next to each other).
'hibernia' becomes 'erin' (I've seen this in another clue).
'yes' put after 'erin' is 'ERINYES'.
Can you help me to learn more?
(Other definitions for erinyes that I've seen before include "Fury repeatedly" , "Snake-haired creatures" , "Monsters" , "Furies (Greek myth)" , "Snake-haired goddesses" .)