Skirt appearing in G&S finds justification (7)
I believe the answer is:
grounds
'justification' is the definition.
(I know that grounds is a type of justification)
'skirt appearing in gs' is the wordplay.
'skirt appearing' becomes 'round' (I am not sure about this - if you are sure you should believe this answer much more).
'in' is an insertion indicator.
'round' going into 'gs' is 'GROUNDS'.
'finds' acts as a link.
Can you help me to learn more?
(Other definitions for grounds that I've seen before include "Coffee sediment" , "Dregs" , "reason" , "Area of enclosed land around a building" , "Reasons" .)