Kaido

Japanese: 海道 - かいどう

[1] 〘 noun 〙① A sea route. Sea route. Ship route . [Iroha Jiruishō (1177-81)] [New Book of Tang - Lu Jun Biography]② A road along the sea. A road leading to various regions along the sea. Also, the area along that road. ※Shoku Nihongi - Jinki 1st year (724) March Koshin "Mutsu Province: Emishi rebellion on the Kaido. _{The second} chief officer, Junior Sixth Rank, Saeki no Sukunekoyamaro _, was killed."③ = Kaido (highway) ※Toraakirahon Kyogen - Dontaro (late Muromachi period - early early modern period) "You and I went out to the Kaido, and we thought that we should stop you." [2] Specifically, it refers to the Tōkaidō. ※Heike (before the 13th century) 5 "The Courtesans and Prostitutes of the Inns along the Kaido" [Eloquence] (1) In the old days, "kairo" was often used to express (1)①, and "kaido" mainly meant ②. Since the Middle Ages, the route between Kamakura and Kyoto became the most important, so "kaido" came to mean the Tokaido. Gradually, the awareness of it as a proper noun faded, and the general noun (1)③, meaning a busy main road, was established.
(2) Based on this, routes were given names such as "Nikko Kaido" and "Koshū Kaido." However, because these routes were far from the sea, the character "海" (sea) came to be felt to be inappropriate, and they came to be written as "街道."

Sea Road [Sea Route]

(From the meaning of a road along the sea) Old name of the Tokaido (highway and the area along the road). Umetsu-michi. Ubetsu-michi. Umitsuji. ※Mitohon Hei Nihongi Shiki (1678) by Emperor Sujin "Tokaido Umitsumi-chi (Umitsumi-chi) "

Source: The Selected Edition of the Japanese Language Dictionary About the Selected Edition of the Japanese Language Dictionary Information

Japanese:

[1] 〘名〙① 海上の航路。海路。船路(ふなじ)。〔色葉字類抄（1177‐81）〕〔新唐書‐盧鈞伝〕② 海沿いの道。海沿いの諸地方に通ずる道。また、その道に沿った地域。※続日本紀‐神亀元年（724）三月甲申「陸奥国言。海道蝦夷反。殺_二大掾従六位上佐伯宿禰児屋麻呂_一」③ ＝かいどう（街道）※虎明本狂言・鈍太郎（室町末‐近世初）「そなたとわらはと中なをりをして、海道へ出でて、あふたらはとめうとぞんずるが」[2] 特に、東海道をいう。※平家（１３Ｃ前）五「海道宿々の遊君遊女ども」[語誌](1)古くは(一)①を表わすには「海路」が多く使われ、「海道」は主として②の意だった。中世以降、鎌倉━京都の往還が最重要路線となったため、「海道」といえば東海道を指すようになったが、次第に固有名詞という意識が薄くなり、人通りの多い〈主要道〉という一般名詞(一)③が確立した。
(2)これに基づいて「日光海道」「甲州海道」などの名付けが行なわれたが、これらが海から遠いため、今度は「海」字が不適当と意識されるようになり、「街道」と書かれるようになった。