Case of nun infiltrating peak event for ladies (3,5)
I believe the answer is:
hen night
'event for ladies' is the definition.
I know nothing about this answer so I can't judge whether this works.
'case of nun infiltrating peak' is the wordplay.
'case of' says to hollow out the word (remove centre letters) (like emptying a case).
'infiltrating' indicates putting letters inside.
'peak' becomes 'height' (synonyms).
'nun' with its middle removed is 'nn'.
'nn' placed within 'height' is 'HEN NIGHT'.
Can you help me to learn more?
(Other definitions for hen night that I've seen before include "Bride's celebration before wedding" , "Amusing the girls, bash" , "Bridal celebration" , "Bride-to-be's party" , "Party for women only" .)