Answer
Not a monomial (the variable has a negative exponent).
Work Step by Step
A monomial is an expression of the form $ax^{k}$,
where $x$ is the variable, the exponent $k$, a nonnegative integer, is the degree,
and $a$ is the coefficient of the term.
Here we have:
$k=-3$,
$k$ is negative so the expression is not a monomial.
