Boy with Yankee noblewoman (4)
I believe the answer is:
lady
'noblewoman' is the definition.
(I know that noblewoman can be written as Lady)
'boy with yankee' is the wordplay.
'boy' becomes 'lad' (informal term for boy).
'with' means one lot of letters go next to another.
'yankee' becomes 'Y' (phonetic alphabet: alpha, bravo, charlie etc.).
'lad'+'y'='LADY'
(Other definitions for lady that I've seen before include "Female title" , "See 7" , "See 19" , "Noble" , "Wife of gentleman" .)