Curlicue is slightly plain, perhaps? (8)
I believe the answer is:
flourish
'curlicue' is the definition.
(thesaurus)
'is slightly plain perhaps?' is the wordplay.
I cannot really see how this works, but
'is' is found in the answer.
This explanation may well be incorrect...
(Other definitions for flourish that I've seen before include "Wax" , "Prosper - display" , "Grow vigorously and healthily" , "Fanfare!" , "Large vase, pot" .)