It's all over dad's shirt tail! (4)
I believe the answer is:
past
'it's all' is the definition.
I can't tell whether this defines the answer.
'over dad's shirt tail' is the wordplay.
'over' is a charade indicator (letters next to each other).
'dad's' becomes 'pas' ('pa' can be a synonym of 'dad').
'tail' says to take the final letters.
The last letter of 'shirt' is 't'.
'pas' put next to 't' is 'PAST'.
Can you help me to learn more?
(Other definitions for past that I've seen before include "historical times" , "Yesteryear" , "Finished, gone" , "Ended" , "Second visitor in 5 [A CHRISTMAS CAROL]" .)