Wailing spirit of Irish folklore (7)
I believe the answer is:
banshee
'wailing spirit of irish folklore' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for banshee that I've seen before include "'Wailing woman, warns of impending death (7)'" , "Sign of imminent death" , "Gaelic spirit" , "Death-portending spirit" , "Irish female spirit who warns of an impending death" .)