In this paper, the definition Rhombic numerical radius is introduced and we present several numerical radius inequalities. Some applications of these inequalities are considered as well. Particular, it is shown that, if $A\in \mathcal B \left( \mathcal{H} \right)$ with the Cartesian decomposition $A=C+iD$ and $r\geq 1$, then \[\begin{aligned} mega^r(A)eq\frac{qrt{2}}{2}{ eftVertvert C+D\rvert^{2 r}+vert C-D\rvert^{2 r}\right\rVert}^{\frac{1}{2}}. \end{aligned}\]