葛飾
Katsushika
(adorned with kuzu)

葛 | kuzu | Japanese Arrowroot, a reed-like grass that grows in wetlands |
飾 | shika | decoration, ornament, embellishment |
This is a very ancient name.
The former 下総国葛飾郡 Shimōsa no kuni Katsushika-gun Katsushika District, Shimōsa Province consisted of areas that are today Tōkyō, Chiba, Ibaraki, and Saitama. This wide area comprised the modern areas of: to the north, Katsushika District, Saitama Prefecture; to the west, Sumida Ward and the eastern half of Kōtō Ward, Tōkyō Metropolis; to the east, Koga City, Ibaraki Prefecture; and to the south, Edogawa Ward, Tōkyō and Urayasu City, Chiba Prefecture.

The name is attested in the 万葉集 Man’yōshū so we know this is an ancient name[i]. The probability of it not being Japanese in origin is high. As mentioned in previous articles, the kanji used in pre-Edo Period Tōkyō place names should always be taken with a grain of salt[ii].
There are various theories, but none of them are certain.
Theory One
Katsushika’s かつ katsu comes from an older word カテ kate or カト kato which meant cliff, hill, or knoll. しか comes from an older スカ which meant “sandbar.” The general idea being that this name referred to the lowlands on the right bank and the elevated ridge on the left bank of the 利根川 Tonegawa Tone River (present day 江戸川 Edogawa Edo River[iii]).
Theory Two
The name was given to the area by the “people of the south sea”[iv]. According to this theory, in whatever dialect or language these people spoke it referred to a hunting ground.
Theory Three
The kanji is literal. 葛 katsu is an on’yomi[v] and nanori[vi] of kuzu arrowroot. 飾 shika is the nanori of kazaru to decorate. Arrowroot is a kind of vine that grows near rivers. It’s an invasive plant that quickly spreads and takes over an area. It is used to make some kinds of jellies for Japanese sweets. If this etymology is accepted, the meaning is then literally “a field or area decorated (overgrown with) Japanese Arrowroot.”

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[i] The Man’yōshū is an ancient text written in a kind of ateji. Here is an article on the text. Here is an article on ateji.
[ii] The kanji used in the Man’yōshū – which are all ateji – are 勝鹿 win + deer and 勝牡鹿 win + male deer and 可豆思賀 nice + bean + think + auspicious. These kanji are meaningless and don’t give any indication of etymology.
[iii] This river was famous for changing course after major floods and tsunamis until the area was wealthy enough to implement proper urban planning. The present Edogawa flows through the ancient course, emptying into Edo Bay (Tōkyō Bay).
[iv] 南洋系の民族 nan’yō-kei no minzoku people from the south sea is a mysterious term that may refer to other immigrant groups coming from the south, or may be a direct reference to the spread of Yamato culture, or may refer to older Yayoi or even Ainu people who just moved into the area at some point. I find this explanation ridiculously unclear – it’s obviously over my head.
[v] The Chinese reading of the kanji.
[vi] A set of common readings of a kanji used in names.