I have a list of keywords and descriptions for those keywords. I would like to have tables for the different contexts in which these are used, containing only the relevant ones for the case. Some of these keywords repeat on the different contexts, so it would be ideal to write the description only once and then "reference" that description in each of my tables for ease of maintenance.

Example:

section{Runtype 1 description}

begin{table}

begin{center}

begin{tabular}{ l l }

runtype & Keyword to determine runtype. Can be 1 or 2. \

        & I don't want to hardcode this description twice...\

param_1 & Keyword to determine the parameter of runtype = 1 \

end{tabular}

end{center}

end{table}



section{Runtype 2 description}

begin{table}

begin{center}

begin{tabular}{ l l }

runtype & Keyword to determine runtype. Can be 1 or 2. \

        & I don't want to hardcode this description twice...\

param_2 & Keyword to determine the parameter of runtype = 2 \

end{tabular}

end{center}

end{table}

Below, I'm defining the following commands:

• 
  setkeyword{<keyword>}{<description>} can be used to declare a keyword.


• 
  getkeyword{<keyword>} retrieves the description you provided.


• 
  keywordtable{<key1>,<key2>,…} displays a table containing the descriptions corresponding to a comma-separated list of keywords.

(Note that keywords containing underscores are allowed.)

documentclass{article}



usepackage[T1]{fontenc} %% <- necessary for _ to be displayed correctly

usepackage{etoolbox}    %% <- for csuse, csdef, ifcsdef and forcsvlist



%% Define/retrieve a new keyword:

newcommandsetkeyword[2]{csdef{keyw@#1}{#2}}

newcommand*getkeyword[1]{%

  ifcsdef{keyw@#1}{%                %% <- if the key is defined...

    csuse{keyw@#1}%                 %% <- return the description

  }{%                                %% <- otherwise...

    ??%                              %% <- question marks

    %errmessage{Undefined key: #1}% %% <- or an ERROR, if you prefer

  }%

}



%% Display a table describing a list of keywords:

newcommand*keywordtable[1]{%

  begin{tabular}{lp{8cm}}

    forcsvlist{tableentry}{#1} %% <- apply tableentry to each value in #1

  end{tabular}%

}

newcommand*tableentry[1]{%

    formattableentry{detokenize{#1}}{getkeyword{#1}}%

}

newcommandformattableentry[2]{ #1 & #2 \ }



% %% Declaration of keywords:

setkeyword{runtype}{Keyword to determine runtype. Can be 1 or 2. par

                     I don't want to hardcode this description twiceldots}

setkeyword{param_1}{Keyword to determine the parameter of runtype = 1}

setkeyword{param_2}{Keyword to determine the parameter of runtype = 2}



begin{document}



section{Runtype 1 description}

keywordtable{runtype,param_1}



section{Runtype 2 description}

keywordtable{runtype,param_2}



end{document}

Some remarks

• 
  setkeyword{<keyword>}{<description>} effectively defines keyw@<keyword> for you, so that it expands to <definition>. You can't use this macro directly because its name contains an @.


• 
  getkeyword{<keyword>} just calls keyw@<keyword>.


• I'm using the e-TeX primitive detokenize to print the keyword. This command strips all tokens in its argument of their special meaning (by changing their catcodes), so you can for instance use detokenize{param_1} safely.


• Without usepackage[T1]{fontenc}, underscores are displayed as " ̇", rather than as "_". You'll probably want to use this package anyway because of the reasons outlined here.


• I'm using tabularx to create a table that has the same width as the current line width. You can replace linewidth by some other value if you want a different width (or just use tabular, in which case you should replace the X column type by something else).

A more customisable version

By request, here is the most customisable version I can think of. This lets you create keywords using setkeyword{<keyword>}{<key1>=<value1>,<key2>=<value2>,…} and retrieve them using getkeyword{<keyword>}{<key>}.
You can create a table with rows corresponding a set of keywords and columns corresponding to specific keys using

keywordtable[<key1>,<key2>,…]{<keyword1>,<keyword2>,…}

I'm using pkgkeys, which is documented in section 82 of the pgf manual.

documentclass{article}



usepackage[T1]{fontenc} %% <- necessary for _ to be displayed correctly

usepackage{pgfkeys}     %% <- for everything starting with pgf

usepackage{etoolbox}    %% <- for forcsvlist



newcommand*{declarekeyword}[1]{%

  pgfkeys{

    /keyw/#1/.is family,

    /keyw/#1/.unknown/.style = {pgfkeyscurrentpath/pgfkeyscurrentname/.initial={##1}},

  }%

}

newcommandsetkeyword[2]{%

  declarekeyword{#1}%

  pgfkeys{/keyw/#1/.cd,name=detokenize{#1},#2}%

}

newcommand*getkeyword[2]{pgfkeysvalueof{/keyw/#1/#2}}



%% Display a table describing a list of keywords:

newcommand*keywordtable[2][name,description]{%

  begin{center}

    begin{tabular}{forcsvlist{getkeyword{@alignment}}{#1}}

      forcsvlist{tableentry[bfseries]{#1}}{@headings}

      forcsvlist{tableentry{#1}}{#2}

    end{tabular}

  end{center}%

}

newcommand*tableentry[3]{%

    letkeywcolsepempty

    forcsvlist{keywcolsepdefkeywcolsep{&}formattableentry[#1]{#3}}{#2}\

}

newcommand*formattableentry[3]{#1{getkeyword{#2}{#3}}}



%% "Fake" keywords (control column titles and alignment)

setkeyword{@headings}{name=Parameter,description=Description,value=Value}

setkeyword{@alignment}{name=l,description=l,value=r}



%% Declaration of keywords:

setkeyword{runtype}{description=A parameter,value=1}

setkeyword{param_1}{description=Another parameter,value=0}

setkeyword{param_2}{name=detokenize{PARAM_2},description=A third parameter,value=42}



begin{document}



section{Runtype 1 description}

keywordtable{runtype,param_1}



section{Runtype 2 description}

keywordtable[name,value,description]{runtype,param_2}



end{document}

documentclass[12pt]{article}

newcommandzzz{%

  runtype & Keyword to determine runtype. Can be 1 or 2. \

          & I don't want to hardcode this description twice...}

begin{document}

section{Runtype 1 description}

begin{table}[ht]

begin{center}

begin{tabular}{ l l }

zzz\

param_1 & Keyword to determine the parameter of runtype = 1 \

end{tabular}

end{center}

end{table}



section{Runtype 2 description}

begin{table}[ht]

begin{center}

begin{tabular}{ l l }

zzz\

param_2 & Keyword to determine the parameter of runtype = 2 \

end{tabular}

end{center}

end{table}

end{document}

It depends on where you want to first key the description you want to repeat.

Probably the best place is in the document preamble or in an external file that you can input.

documentclass{article}

usepackage{xparse}



% a few line of code for setting up the system

ExplSyntaxOn



NewDocumentCommand{newdesc}{mm}

 {% #1 is a key, #2 is the description

  prop_gput:Nnn g_nordico_descriptions_plist { #1 } { #2 }

 }



NewDocumentCommand{getdesc}{m}

 {% #1 is a key

  prop_if_in:NnTF g_nordico_descriptions_plist { #1 }

   { prop_item:Nn g_nordico_descriptions_plist { #1 } }

   { ???~non~existent~description~??? }

 }



prop_new:N g_nordico_descriptions_plist



ExplSyntaxOff



% the descriptions (they can go in an external file

% say desc.tex and here you'd do input{desc}



newdesc{A}{I don't want to hardcode this description twice...}



begin{document}



section{Runtype 1 description}

begin{center}

begin{tabular}{ l l }

runtype  & Keyword to determine runtype. Can be 1 or 2. \

         & getdesc{A} \

param_1 & Keyword to determine the parameter of runtype = 1 \

end{tabular}

end{center}



section{Runtype 2 description}

begin{center}

begin{tabular}{ l l }

runtype  & Keyword to determine runtype. Can be 1 or 2. \

         & getdesc{A} \

param_2 & Keyword to determine the parameter of runtype = 2 \

end{tabular}

end{center}



end{document}

Note that it is not at all necessary to place a tabular in a floating table environment (which might make the tabular go to another page).