Etonian pal mistaken for an Italian (10)
I believe the answer is:
neapolitan
'for an italian' is the definition.
(I've seen this before)
'etonian pal mistaken' is the wordplay.
'mistaken' indicates an anagram.
'etonian'+'pal'='etonianpal'
'etonianpal' anagrammed gives 'NEAPOLITAN'.
(Other definitions for neapolitan that I've seen before include "One coming from Campania" , "21 [ITALIAN]" , "chocolate" , "Three-coloured ice cream" , "Italian native" .)