\documentclass[a4paper,twoside]{article}

%\usepackage[style=long,cols=3,border=plain]{glossary}
\usepackage{makeglos}
\makeglossary

\begin{document}
\printglossary

\begin{description}
\item [This is the item] The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long.
\item [This is the other item] The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long.
\end{description}

\glossary{This it the item:The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long. The description for this item can be very long.}

\glossary{glossary:item}

\end{document}