Foolishly, short professor tore into nun and, at this stage, there's no going back (5,2,2,6)
I believe the answer is:
point of no return
'foolishly short professor' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'tore into nun and at this stage there's no going back' is the wordplay.
I cannot really understand how this works, but
an anagram of 'tore' is 'oret' which is located in the answer.
an anagram of 'into' is 'oint' which is located in the answer.
'and' could be 'n' (common abbreviation for 'and') and 'n' is found in the answer.
'there's' could be 'n' (I've seen this in other clues) and 'n' is present in the answer.
'no' could be 'o' (O resembles 0) and 'o' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for point of no return that I've seen before include "ace played?" , "after which one's committed?" , "After which one can't go back" , "Crucial moment" .)