Radical 17
Radical 17 or radical open box is one of 23 of the 214 Kangxi radicals that are composed of two strokes.
凵 is also the 20th indexing component in the Table of Indexing Chinese Character Components predominantly adopted by Simplified Chinese dictionaries published in mainland China.
In the Kangxi Dictionary, there are 23 characters to be found under this radical.
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".
Derived characters
The radical does not occur as a character on its own. In combination, it historically takes meanings such as "open mouth", "box", "frame", "hole" or "receptacle".Also derived from the radical are the Simplified Chinese characters including "to hit", without any historical connection to the radical.
"deep, dark" is derived from radical 46 rather than radical 17.