My dear, it's silly to be romantic! (6)
I believe the answer is:
dreamy
'romantic' is the definition.
(thesaurus)
'my dear it's silly' is the wordplay.
'it's silly' indicates anagramming the letters.
'my'+'dear'='mydear'
'mydear' anagrammed gives 'DREAMY'.
'to be' is the link.
(Other definitions for dreamy that I've seen before include "My dear (anag.)" , "Vague - pensive" , "Fantastic" , "Lovely" , "romantic" .)