Girl goes on an excursion (5)
I believe the answer is:
sally
'an excursion' is the definition.
(I've seen this before)
'girl goes' is the wordplay.
'girl' becomes 'sal' (feminine given name).
'goes' becomes 'ly' (I can't explain this - if you can you should believe this answer much more).
'sal'+'ly'='SALLY'
'on' acts as a link.
Can you help me to learn more?
(Other definitions for sally that I've seen before include "Sortie - Gracie Fields song" , "excursion" , "Witty riposte" , "- - Lunn, flat cake" , "army" .)