Youngster of frugality (3)
I believe the answer is:
gal
'youngster' is the definition.
'of frugality' is the wordplay.
'of' indicates the answer is hidden within the clue.
'GAL' is hidden within 'frugality'.
(Other definitions for gal that I've seen before include "US female" , "measure of acceleration?" , "female noted in Kalamazoo" , "Girl from American west" , "Young woman (colloq.)" .)