The same symbol can name both a lexical variable and a dynamic variable, but never in the same lexical environment.
In the following example, the symbol x is used,
at different times,
as the name of a lexical variable
and as the name of a dynamic variable.
(let ((x 1)) ;Binds a special variable X
(declare (special x))
(let ((x 2)) ;Binds a lexical variable X
(+ x ;Reads a lexical variable X
(locally (declare (special x))
x)))) ;Reads a special variable X
⇒ 3