A dandy, too (2,4)
I believe the answer is:
'too' is the definition.
('as well' can be a synonym of 'too')
'a dandy' is the wordplay.
'dandy' becomes 'swell' ('swell' can be a synonym of 'dandy').
(Other definitions for as well that I've seen before include "with equal effect" , "on top" , "A swell sort of addition" , "Appropriate" , "Also, in addition" .)