Pages about American, mythical being (7)
I believe the answer is:
pegasus
'mythical being' is the definition.
(Pegasus is an example)
'pages about american' is the wordplay.
'about' indicates an anagram.
'american' becomes 'us' (abbreviation for United States).
'pages' anagrammed gives 'pegas'.
'pegas'+'us'='PEGASUS'
(Other definitions for pegasus that I've seen before include "Winged horse of Greek myth" , "Mount flying" , "group of stars" , "Exceptional horse" , "Mythological horse" .)