穴

A void, hollow, or aperture within a solid mass (typically earth or rock). This includes geological features (cave, cavern, grotto), biological dwellings (burrow, den, lair), and anatomical/medical contexts (acupuncture points).

Functions almost exclusively as a noun. If the glyph appears to function as a verb, it may be an idiosyncratic usage or a misreading of a similar glyph such as 掘.

Compared to other "hole" glyphs: 洞 typically implies a passage or a perforated opening that leads through something; 窟 carries a stronger connotation of habitation (a lair or hideout); 坑 usually refers to a pit, trench, or excavated depression.

Kangxi radical 116.

Avoid the reflexive use of "cave," which may impose a specific scale or atmospheric quality not present in the source. Depending on context, "hollow," "aperture," "burrow," or "point" may be more accurate.