[aaco]

"... but it's not a Lisp ..."

It is.

"... pure Lisp ..."

There is no such a thing as "pure Lisp". Lisp is not a programming language, it's a family of programming languages that share some common properties.

To put it more clearly, we could represent Lisp and its members hierarchically:

    Lisp
        Common Lisp
            CLISP
            SBCL
            ...
        Scheme
            Racket
            Gambit
            Chicken
            ...
        Clojure
        ...