Tsukumogami (付喪神 or つくも神?, "Tool kami") are tools that have acquired a spirit living in them after many years. They deceived humans. Also, according to an annotated version of The Tales of Ise titled Ise Monogatari Shō, a certain theory in the Onmyōki, tsukumogami are what foxes that have lived for one hundred years turn into. In modern times, they can also be written 九十九神 (ninety-nine kami).
According to Komatsu Kazuhiko, the idea of tsukumogami, or yōkai of tools, spread mostly in the Middle Ages, and declined in more recent generations. Komatsu infers that despite the depictions in Bakumatsu period ukiyo-e leading to a resurfacing of the idea, these were all produced in an era cut off from any actual belief in the idea of tsukumogami.
For "tsukumogami" to have the kanji representation 付喪神 comes from the Tenpō period otogizōshi, the emakimono called the Tsukumogami Emaki. According to this emaki, a tool, after the passage of 100 years, would obtain a spirit, and a tsukumogami is a result of this change or mutation. In this emaki, there was also a caption that "tsukumo" could also be written as 九十九 (meaning "ninety-nine") referring to "one year before one hundred," and made the interpretation that this meaning came from "tsukumo hair" (つくも髪, pronounced tsukumogami), a word that appeared in a waka in The Tales of Ise, section 63 to refer to an old woman's white hair, which is why tsukumo means "a long time (ninety-nine years)."
Other than the "Tsukumogami Emaki" and interpretations made in annotated versions of The Tales of Ise waka poems of the words "tsukumogami" (つくも髪, tsukumo hair), usages of the word "tsukumogami" do not appear anywhere in literature, and usages of it has not been transmitted in detail. In collections of tales such as the Konjaku Monogatarishū, there were tales that could be seen to be about objects having a spirit, and in the emakimono Bakemono Zōshi, there were tales depicting a chōshi (an alcohol cup), a scarecrow, and other things turn into monsters, but there was no word "tsukumogami" mentioned in them.