  An active optical clock based on highly charged Nd$^{9+}$ ion is proposed for
the first time. The clock can offer ultra-narrow linewidth at the
$\upmu$Hz-level which is more than two-order of magnitude below the currently
recorded laser linewidth. Operating at 605(90) nm superradiation lasing
transition between the $5p^2~4f$ ground state and one of the long-lived
$5p~4f^2$ excited state, the proposed active clock is inherently immune against
the cavity noise which provides high stability. The clock serves as a sensitive
probe with high sensitivity to variation of the fine-structure constant with
accuracies below 10$^{-19}$ level. Sophisticated relativistic many-body methods
are employed to predict related atomic properties that have corroborated the
above findings.
