documentclass{article}
usepackage{fontspec}
usepackage{xparse}
usepackage{tikz}
newcounter{itemcounter}
NewDocumentCommand{itemcount}{}{addtocounter{itemcounter}{1}arabic{itemcounter}}
NewDocumentCommand{tmark}{ m }{tikz [remember picture,overlay] node [draw] (#1) {};} % used in definition of item

%Some fancy schmancy code to transform the following item:
%item [item] Some text.
%into this:
%item [tmark{nodeprefixitemcount}] Some text. %expands to [tikz [remember picture, overlay] node [draw] (lista1) {};]

begin{document}
begin{description}[nodeprefix=lista] % Not sure how to make a key or pass value of it to macro nodeprefix
  item [Apple] This is a fruit.
  item [Broccoli] This is a vegetable.
end{description}
begin{description}[nodeprefix=listb] % Not sure how to make a key or pass value of it to macro nodeprefix
  item [Silver] This is a solid.
  item [Water] This is a liquid.
end{description}
begin{description}[nodeprefix=listc] % Not sure how to make a key or pass value of it to macro nodeprefix
  item [Happiness] This is a state of being.
  item [Sadness] This is an unfortunate state of being.
end{description}
end{document}

node (lista1) {};
node (lista2) {};
node (listb1) {};
node (listb2) {};
node (listc1) {};
node (listc2) {};

makeatletter % Redefine description list http://tex.stackexchange.com/a/66386/13552
renewenvironment{description}
  {
  list{}{labelwidthz@ itemindent-leftmargin
   letmakelabeldescriptionlabel}
  }
  {
  endlist
  }
  letdescriptionlabelrelax
newcommand*descriptionlabel[1]{hspacelabelsepnormalfontbfseries #1}
makeatother

expandafterdefexpandafterdescriptionexpandafter{% http://tex.stackexchange.com/a/230316/13552
  description letolditemitem
  defitem[##1]{olditem[##1]mbox{}\}}