begin{document}
  This (1) is (2).

  (1: book)
  (2: good)
end{document}

«This book is good.»

documentclass{article}
defmylabel(#1: #2){expandafterdefcsname MY#1endcsname{#2}}
defmyref(#1){csname MY#1endcsname}
begin{document}
  mylabel(1: book)
  mylabel(2: good)

This myref(1) is myref(2).
end{document}

documenclass{article}
newcommandsubA{book}
newcommandsubB{good}

begin{document}
This subA{} is subB.
end{document}