Sharp alpha male, whimsical Australian mostly on the inside (10)
I believe the answer is:
astringent
'inside' is the definition.
Both the definition and answer are adjectives. Maybe they are linked in a way I don't understand?
'sharp alpha male whimsical australian mostly on the' is the wordplay.
'sharp alpha male whimsical australian' becomes 'astringe' (I can't justify this - if you can you should give a lot more credence to this answer).
'mostly' means to remove the first letter (a).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'on' with its initial letter taken off is 'n'.
'astringe'+'n'+'t'='ASTRINGENT'
Can you help me to learn more?
(Other definitions for astringent that I've seen before include "Styptic" , "Harsh" , "for checking bleeding" , "description of wine?" , "medical preparation" .)