\documentclass[a4paper]{report}
\usepackage[]{glossaries}
%\usepackage[footnote]{glossaries}
\makeglossaries
\newacronym[longplural={areas of outstanding natural beauty}]{AONB}{AONB}{area of outstanding natural beauty}

\begin{document}
\begin{itemize}
\item \glspl{AONB}
\item \gls{AONB}
\item \glsplural{AONB}
\item \glsfirst{AONB}
\item \glsfirstplural{AONB}
\item \Glsfirst{AONB}
\item \Glsfirstplural{AONB}
\end{itemize}
\end{document}

