Secret Words

...a special word with a sense of secrecy that is only used by members of a certain social class or occupation. Originally it was called "hidden words," but as a result of the use of the character "hidden words" (argot), it came to be called "ingo," and it was also used as a translation of slang, and the meaning and content of the word "argot" became complex. Since slang is an informal language that is only used among friends, it is not limited to the words of antisocial groups such as samurai and criminals, but also includes the "Itsuki no Miya Imikotoba" of the Heian period shrines (Araraki for tower, Kaminaga for priest, Nazu for uchi, etc.), the "Nyobo-kotoba" of court ladies (Oden for dengaku, Shamoji for ladle, Okabe for tofu, etc.), the "Gakurin-higo" of monks (Shironas for eggs, Kamisori for sweetfish, Gomasu for sake, etc.), the "Senbo" used by Osaka puppeteers (Sentarou for money, etc.), the "Oki-kotoba" of fishermen, and the "Yama-kotoba" of hunters, etc., can also be considered slang in a broad sense.

*Some of the terminology explanations that mention "hidden words" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…特定の階層や職業の社会集団だけにしか通用しない秘密性を帯びた特殊な言葉。元来は〈かくしことば〉といったが，隠語の字をあてられた結果〈いんご〉と呼ばれるようになり，スラングslangの訳語ともされて，隠語の意義内容は複雑になった。隠語は仲間うちだけに通用する目的の非公式の言葉であるから，香具師（やし）や犯罪者等の反社会的集団のものだけにかぎらず，平安時代の神宮の〈斎宮忌詞（いつきのみやいみことば）〉(塔をアララキ，僧をカミナガ，打つをナヅなど)，宮廷女官の〈女房言葉〉(田楽をオデン，杓子をシャモジ，豆腐をオカベなど)，僧侶の〈学林秘語〉(卵をシロナス，鮎をカミソリ，酒をゴマスなど)，大阪の人形遣いの用いた〈占傍（せんぼう）〉(金銭をセンタロウなど)，漁師の〈沖言葉〉や猟師の〈山言葉〉なども広い意味で隠語といえる。…

※「かくしことば」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報