Fancy panties -- is that wise? (7)
I believe the answer is:
sapient
'that wise?' is the definition.
(thesaurus)
'fancy panties' is the wordplay.
'fancy' is an anagram indicator.
'panties' with letters rearranged gives 'SAPIENT'.
'is' acts as a link.
(Other definitions for sapient that I've seen before include "Panties (anag)" , "Literary word for wise" , "Discerning" , "Having intelligence" , "very keen" .)