The method of collating words according to their first syllable with semantic subdivisions had been established as early as at the end of the Heian period (during the period of government by the retired Emperor) as represented by "Irohajiru sho" (one of Japanese dictionaries in the Heian period) and its supposedly enlarged edition, "Irohajirui-sho" (a dictionary written by Tadakane TACHIBANA in Heian period).
頭文字で分類しかつ意味で部門分けする形式は早く平安時代末期（院政期）成立の『色葉字類抄』と、その増補と見られる『伊呂波字類抄』がある。