Horn (music) - Kaku

Japanese: 角（音楽） - かく

…Also called five tones. The five scale notes set in one octave, namely, Gong (miya), Shang, Kaku, Chi, and Yu (yu). Originally a term introduced from China, it was Japanized, and the first note of the five-tone scale is always Gyou regardless of the key, and the notes going up are Shang, Kaku, etc. …

From [Five Tones]

…It is the basis of the Chinese scale, and was introduced to Japan and Korea. It consists of five tones: Gong, Shang, Jiao, Zheng, and Yu. The seven tones include the inflections Zheng and Zheng, which are half a tone lower than Gong. The five tones were used in China from the end of the Zhou Dynasty to the Western Han Dynasty, and are described in works such as the Guanzi, the Spring and Autumn Annals of the Lü Family, and the Huainanzi. …

From [Horn]

...the common name for various wind instruments that use animal horns in almost their original form to create sound. In a broad sense, it also includes instruments that are their descendants.

*Some of the terminology explanations that mention "horns (music)" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…五声ともいう。1オクターブの中に設定される五つの音階音，すなわち宮（きゆう），商，角，徴（ち），羽（う）をいう。元来は中国から伝えられた用語が，日本化したもので，5音音階の第1音を調に関係なくつねに宮とし，上に向かって順に商，角……とする。…