Girl's beginning to enter with no clothes on — that may be to attract attention (5)
I believe the answer is:
'clothes on that may be to attract attention' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'girl's beginning to enter with no' is the wordplay.
'beginning to' says to take the initial letters.
'enter' means one lot of letters goes inside another.
'with no' becomes 'nude' (I can't justify this - if you can you should believe this answer much more).
The initial letter of 'girls' is 'g'.
'g' going within 'nude' is 'NUDGE'.
Can you help me to learn more?
(Other definitions for nudge that I've seen before include "Push with the elbow" , "Festive entertainment" , "Elbow someone gently" , "Shove" , "Prod gently with elbow" .)