How can I create a glossary as I go?

Question

I'd like to keep defining terms as I go through the document using the description environment, but then have all those terms gathered together (with their descriptions) in a glossary at the end of the document.

The glossaries package would seem to be the obvious choice for how to do this, but I can't see a way to list the entry descriptions in the document body as I go. An MWE would look like

\documentclass{article} 
\usepackage[utf8]{inputenc} 
\usepackage{blindtext} 
\begin{document} 
\tableofcontents{} 
\section{Introduction}
    \begin{description}
    \item[Ontology] refers to a theory of what is real
    \item[Epistemology] refers to a theory of knowledge
    \end{description}
     \section{Theory} \begin{description}
    \item[Potato] is a class of root vegetables
    \item[Reductionism] refers to the practice of reducing one set of ideas to another \end{description}

\section{Glossary of Terms}

\begin{description}
    \item[Epistemology] refers to a theory of knowledge
    \item[Ontology] refers to a theory of what is real
    \item[Potato] is a class of root vegetables
    \item[Reductionism] refers to the practice of reducing one set of ideas to another \end{description}

\end{document}

Which looks this:

As in, all the terms from the {description} environment get collected, alphabetised, and reproduced with their descriptions in a glossary of terms.

Answer 1

The simplest method is to create a new file that contains the definitions. This makes it easier to add new terms while you're writing the document as most text editors allow more than one file open at a time, so you can simply switch to the definitions file without losing your place in the document.

Here's definitions.tex:

\newglossaryentry{ontology}{name={ontology},
  description={refers to a theory of what is real}}
\newglossaryentry{epistemology}{name={epistemology},
 description={refers to a theory of knowledge}}
\newglossaryentry{potato}{name={potato},
 category={theory},
 description={is a class of root vegetables}}
\newglossaryentry{reductionism}{name={reductionism},
 category={theory},
 description={refers to the practice of reducing one set
 of ideas to another}}

If your definitions span multiple paragraphs then use \longnewglossaryentry instead:

\longnewglossaryentry{reductionism}{name={reductionism},category={theory}}
{refers to the practice of reducing one set
 of ideas to another}

Here's a document that uses the all the provided definitions:

\documentclass{article}

\usepackage{glossaries-extra}

\loadglsentries{definitions}

\glssetcategoryattribute{general}{glossname}{firstuc}
\glssetcategoryattribute{theory}{glossname}{firstuc}

\newcommand{\printcategory}[1]{%
  \printunsrtglossary*{%
    \renewcommand{\glossarysection}[2][]{}%
    \renewcommand{\printunsrtglossaryhandler}[1]{%
      \glsifcategory{##1}{#1}{\glsxtrunsrtdo{##1}}{}%
    }%
  }%
}

\begin{document}
\tableofcontents

\section{Introduction}
\printcategory{general}

\section{Theory}
\printcategory{theory}

\printunsrtglossary[title={Glossary of Terms}]

\end{document}

If the document is called myDoc.tex then the document build is simply:

pdflatex myDoc

This lists all defined terms in the glossary in the order of definition. If you want the list sorted, then it's more complicated.

Here's an alternative method. Save the definitions in a .bib file, say, definitions.bib:

% Encoding: UTF-8
@entry{ontology,
  name = {ontology},
  description = {refers to a theory of what is real}
}

@entry{epistemology,
  name = {epistemology},
  description = {refers to a theory of knowledge}
}

@entry{potato,
  name = {potato},
  plural = {potatoes},
  description = {is a class of root vegetables}
}

@entry{reductionism,
  name = {reductionism},
  description = {refers to the practice of reducing one set
 of ideas to another}
}

Again, it should be simple to switch back and forth between two windows without losing your place in the document. The document is now:

\documentclass{article}

\usepackage[record,% using bib2gls
  postpunc=dot% put a full-stop after the descriptions in the glossary
]{glossaries-extra}

\GlsXtrLoadResources[
  src={definitions},% entries in definitions.bib
  name-case-change={firstuc}% convert the first character of `name` to uppercase and set `text` to the original value of `name`
]

\newcommand{\glossitem}[1]{\item[\glsentryname{#1}]
 \glsadd{#1}\glsentrydesc{#1}.}

\begin{document}
\tableofcontents

\section{Introduction}
\begin{description}
\glossitem{epistemology}
\glossitem{ontology}
\end{description}

\section{Theory}
\begin{description}
\glossitem{potato}
\glossitem{reductionism}
\end{description}

\printunsrtglossary[title={Glossary of Terms}]

\end{document}

This gives you more manual control over the ordering within the document for the different sections. The main glossary is now sorted and includes locations in the glossary that indicate where the term was used (page 1 in all cases for this trivial document).

The build process is now:

pdflatex myDoc
bib2gls myDoc
pdflatex myDoc

If you don't want the locations, either use the resource option save-locations=false:

\GlsXtrLoadResources[
  src={definitions},% entries in definitions.bib
  name-case-change={firstuc},
  save-locations=false
]

or use nonumberlist:

\printunsrtglossary[title={Glossary of Terms},nonumberlist]

By default bib2gls will sort according to the document language (if detected) otherwise it will sort according to the default locale. You can specify a particular language. For example:

\GlsXtrLoadResources[
  src={definitions},% entries in definitions.bib
  name-case-change={firstuc},
  sort={en-GB}
]

If you want to reference a term anywhere else in the document, you can use \gls{label}, for example \gls{ontology}, or at the start of a sentence \Gls, for example \Gls{potato}. The plural can be obtained with \glspl and \Glspl. If you load hyperref (before glossaries-extra), then these will be turned into hyperlinks to the relevant line in the main glossary.