Thin dish - Usuki

Japanese: 薄器 - うすき

…A general term for containers for thin tea, as opposed to thick tea. Also called thin vessels. A typical example is the natsume, which is said to have originated from the hikiya (protective vessel) used for thick tea, and resembles the shape of a jujube fruit. …

From [Natsume]

…So, while small ceramic jars from China were used as containers for thick tea, Japanese lacquered containers were designed for thin tea. In a broad sense, natsume can be another name for this Japanese thin (tea) vessel. In other words, even if the shape is not necessarily natsume-shaped, it is used as a synonym for thin vessels and as a word that is more suited to the tea ceremony. …

*Some of the terminology that refers to "thin ware" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…濃茶の茶入に対し，薄茶を入れる容器の総称。薄器とも称する。代表的なものを棗（なつめ）といい，これは濃茶入の挽家（ひきや）(保護のための容器)から生じたとされ，ナツメの実に形が似ている。…