疾い

From attributive form of earlier 疾し (toshi). /tosi/ → /toki/ → /toi/.

疾(と)い • (toi) -i (adverbial 疾(と)く (toku))

1. (obsolete) fast, quick
   • 970–999, Utsubo Monogatari, page Toshikage:

     この木のあらむ所たづねて、いかで、琴の声の聞ゆる方に、疾き足をいたして、こはき力をはげみて、海、河、峯、谷を超えて、その年暮れぬ。

     Asking the tree of what's rough, in how, could a koto's way of vibration, affecting a quick foot, still have strong power, through the seas, the rivers, the peaks, as that year has become dark.

• 疾(と)うの昔(むかし) (tou no mukashi, “a long time ago”)

• Kōno, Tama (c. 970–999) Nihon Koten Bungaku Taikei 10: Utsubo Monogatari 1 (in Japanese), Tōkyō: Iwanami Shoten, published 1959, →ISBN.