...cunning and regularly silly (3)
I believe the answer is:
sly
'cunning' is the definition.
(synonyms)
'regularly silly' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternate letters of 'silly' are 'SLY'.
'and' acts as a link.
(Other definitions for sly that I've seen before include "Cunning, foxy" , "Crafty, devious" , "Cunning, deceitful" , "Devious and furtive" , "Cunning; surreptitious" .)