Radical 17
Radical 17 is one of 23 of the 214 Kangxi radicals that are composed of 2 strokes.
It does not occur as a character on its own. In combination, it historically takes meanings such as "open mouth", "box", "frame", "hole". In contemporary use, it is the base radical of the following characters:
凶 "bad, inauspicious"
出 "go out, send out"
函 "box"
Also derived from the radical are the Simplified Chinese characters 击 "to hit" and 画 "to paint", without any historical connection to the radical.
Note that 幽 "deep, dark" is derived from radical 46, "mountain" 山 rather than radical 17.
As for the similar radicals 22 匚 and 13 冂, the name of radical 17 is purely descriptive of its shape, 下三框 "lower three-sided frame".
Characters with Radical 17
Literature
Fazzioli, Edoardo. Chinese calligraphy : from pictograph to ideogram : the history of 214 essential Chinese/Japanese characters. calligraphy by Rebecca Hon Ko. New York: Abbeville Press. ISBN 0-89659-774-1.
Leyi Li: “Tracing the Roots of Chinese Characters: 500 Cases”. Beijing 1993, ISBN 978-7-5619-0204-2