Mild exposure leads to debility entering university: I’m grateful for admission (11)
I believe the answer is:
decolletage
'mild exposure' is the definition.
(an amount of cleavage exposed by a low neckline)
'leads to debility entering university i'm grateful for admission' is the wordplay.
'leads to' says to take the initial letters.
'university' becomes 'college'.
'i'm grateful' becomes 'ta' (both can mean thank you).
'for admission' is an insertion indicator (inserted letters are let in or admitted).
The initial letters of 'debility entering' is 'de'.
'college' enclosing 'ta' is 'colletage'.
'de'+'colletage'='DECOLLETAGE'
(Other definitions for decolletage that I've seen before include "Revealing cut" , "Dress style" , "Low-cut neckline" , "Low neckline" .)