It's not plain talk that enthrals any number (6)
I believe the answer is:
ornate
'it's not plain' is the definition.
'talk that enthrals any number' is the wordplay.
'talk' becomes 'orate' (orating is a kind of talking).
'that enthrals' means one lot of letters goes inside another.
'any number' becomes 'n' (I've seen this in other clues).
'orate' placed around 'n' is 'ORNATE'.
(Other definitions for ornate that I've seen before include "(Of literary style) complex and with unusual words" , "Over-decorated" , "Are not (anag.)" , "Sumptuously decorated" , "Ostentatious" .)