Xu Shen
The smallest category of characters is also the least understood. In the postface to the ', Xu Shen gave as an example the characters ' "to verify" and "" "old", which had similar Old Chinese pronunciations (*khuʔ and *C-ruʔ respectively) and may once have been the same word, meaning "elderly person", but became lexicalized into two separate words. The term does not appear in the body of the dictionary, and is often omitted from modern systems.