Irritatingly, it reminds you of your fall from grace (4,5)
I believe the answer is:
hair shirt
'grace' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for hair shirt that I've seen before include "A penitential garment of hirsute beginnings" , "article for an ascetic" , "Traditional wear of ascetic" , "Hirsute penitential garment for men" , "uncomfortable clothing" .)