"Lush" stands for "Lisp Universal Shell". It has not just S-expression syntax but recursion, setq, dynamic typing, quoting of S-expressions and thus lists and homoiconicity, cons, car, cdr, let*, cond, progn, runtime code evaluation, serialization (though bread/bwrite rather than read/print), and readmacros. Its object system is based on CLOS.

Lush is uncontroversially a Lisp.

However, the part of this that's relevant to the point I was actually making is that Lush uses S-expression syntax, which is less readable than, for example, Python syntax.