A clear note to twin girls (5)
I believe the answer is:
vivid
'a clear' is the definition.
(thesaurus)
'note to twin girls' is the wordplay.
'twin girls' can mean two substitutions for 'girl'.
'note' becomes 'D' (musical note).
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'girl' becomes 'vi' (short for Violet).
'girl' becomes 'vi' (short for Violet).
'vi'+'vi'='vivi'
'd' after 'vivi' is 'VIVID'.
(Other definitions for vivid that I've seen before include "Strong and bright, colour perhaps" , "Fresh and bright" , "Presenting a clear and striking picture" , "Graphic" , "Brilliant" .)