round well curb
Refers to the wooden or stone frame around the mouth of a round well. An archaic word, now mostly known from the famous poem in the Ise Monogatari.
"Tsutsuizutsu" is an old word known from a poem in the Ise Monogatari.
The exact derivation is uncertain; the word is composed of 筒 (tsutsu, 'tube/cylinder') and 井筒 (izutsu, 'well curb'), describing a round well curb.