Where the shape comes from
A box laid on its side, open along one edge — a recess just deep enough to tuck something out of sight. An arrow 矢 slotted into it gives the simplified 医, doctor, from a story in which the earliest medicine was the surgeon’s arrowhead kept ready in its case; something living pressed into the same recess gives 匿, to hide.
汉字 filed under 匸
No published character on HSK Guide is filed under this radical yet. 汉字库.