nothing but; nothing more than; nothing less than
Fixed expression used after a noun to strongly assert that something is exactly that thing and nothing else. Often emphatic.
He is nothing less than a genius.
That is nothing but a lie.
「に過ぎない」 also means 'nothing more than', but is less emphatic and more objective, often used to downplay something. 「以外の何者でもない」 is stronger and more subjective, asserting identity.
Standard kanji-kana spelling for this fixed expression.
Variant with 無い for ない; less common in modern usage.
A fixed emphatic expression composed of 以外 (other than), 何者 (what kind of person/thing), でも (even), and ない (not). Literally 'is not even any other thing than...'.