We report the first observation of the decay ${D}^{+}\ensuremath{\rightarrow}{\ensuremath{\eta}}^{\ensuremath{'}}{e}^{+}{\ensuremath{\nu}}_{e}$ in two analyses, which combined provide a branching fraction of $\mathcal{B}({D}^{+}\ensuremath{\rightarrow}{\ensuremath{\eta}}^{\ensuremath{'}}{e}^{+}{\ensuremath{\nu}}_{e})=(2.16\ifmmode\pm\else\textpm\fi{}0.53\ifmmode\pm\else\textpm\fi{}0.07)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$. We also provide an improved measurement of $\mathcal{B}({D}^{+}\ensuremath{\rightarrow}\ensuremath{\eta}{e}^{+}{\ensuremath{\nu}}_{e})=(11.4\ifmmode\pm\else\textpm\fi{}0.9\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$, provide the first form factor measurement, and set the improved upper limit $\mathcal{B}({D}^{+}\ensuremath{\rightarrow}\ensuremath{\phi}{e}^{+}{\ensuremath{\nu}}_{e})l0.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ (90%C.L.).
