Green lady, terribly romantic (9)
I believe the answer is:
legendary
'romantic' is the definition.
(thesaurus)
'green lady terribly' is the wordplay.
'terribly' indicates an anagram.
'green'+'lady'='greenlady'
'greenlady' with letters rearranged gives 'LEGENDARY'.
(Other definitions for legendary that I've seen before include "Mythical or fabled" , "Mythical - very famous" , "Celebrated in fable" , "Well-known" , "Relating to old or mythological tales" .)