What makes Lisp...Lisp?

If you starting removing features from Lisp, at what point is it no longer Lisp? Some people claim Clojure shouldn't be considered a Lisp. Is it because too much Lisp was removed?

What is at the very heart of Lisp that makes it Lisp?

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There are plenty of small problems that can be solved using dynamic languages and don't need ricer level optimizations. Dynamic languages make things easier to hack together some logic without being bogged down with trivial minutia.