  We determine the characteristic timescales associated with the linearized
relaxation dynamics of the composed
Reissner-Nordstr\"om-black-hole-charged-massive-scalar-field system. To that
end, the quasinormal resonant frequencies
$\{\omega_n(\mu,q,M,Q)\}_{n=0}^{n=\infty}$ which characterize the dynamics of a
charged scalar field of mass $\mu$ and charge coupling constant $q$ in the
charged Reissner-Nordstr\"om black-hole spacetime of mass $M$ and electric
charge $Q$ are determined {\it analytically} in the eikonal regime $1\ll
M\mu<qQ$. Interestingly, we find that, for a given value of the dimensionless
black-hole electric charge $Q/M$, the imaginary part of the resonant
oscillation frequency is a monotonically {\it decreasing} function of the
dimensionless ratio $\mu/q$. In particular, it is shown that the quasinormal
resonance spectrum is characterized by the asymptotic behavior $\Im\omega\to0$
in the limiting case $M\mu\to qQ$. This intriguing finding implies that the
composed Reissner-Nordstr\"om-black-hole-charged-massive-scalar-field system is
characterized by extremely long relaxation times $\tau_{\text{relax}}\equiv
1/\Im\omega\to\infty$ in the $M\mu/qQ\to 1^-$ limit.
