でんぐり返る

Compound of でんぐり (denguri) +‎ 返る (kaeru, “to turn over”).^[1][2] The kaeru changes to gaeru as an instance of rendaku (連濁). Sometimes also pronounced without rendaku and with a hard k sound instead, as dengurikaeru.^[1][2]

The denguri part is of unclear origin. It only appears in this compound and derived forms.

• The den portion is most likely the same den found in terms such as でんでん (denden, “one after the next, rolling, continuous”, adverb), itself also found in the compound でんでん太鼓 (denden-daiko, “denden (rolling? continuous?) drum”, a small taiko drum with a handle extending from the bottom and two small balls attached by short strings to each side as strikers, played by holding in one hand and rapidly twisting the handle back and forth).
• The guri portion is almost certainly 繰り (kuri, “winding, reeling, spinning”), the 連用形 (ren'yōkei, “continuative or stem form”) of verb 繰る (kuru, “to wind, to spin, to reel”).

• (Tokyo) でんぐりがえる (Nakadaka – )^[2]
• IPA^(key):

でんぐり返(がえ)る • (dengurigaeru) intransitive godan (stem でんぐり返(がえ)り (dengurigaeri), past でんぐり返(がえ)った (dengurigaetta))

1. to turn over, to turn upside-down
2. to do a somersault (either forwards or backwards)
3. to be head over heels, to be in disarray, to be very confused

• (turn over): ひっくり返(かえ)る (hikkurikaeru)
• (somersault): でんぐり返(がえ)しをする (dengurigaeshi o suru)
• (somersault): 蜻蛉返(とんぼがえ)りをする (tonbogaeri o suru)