- (geometry) A quadrilateral, usually referred to a square or rectangle.
- A quadrilateral with vertices named A, B, C, and D in order.
- A male family member in a family tree. Compare ○ (“a female family member in a family tree”).
- (logic) logically necessary; provable
- (astrology) quadrature.
- (alchemy) salt.
- See ☐ for a blank ballot.
- (logical necessity): ◊
- Used as a placeholder for an unknown hanzi (such as for a dialectal morpheme).
- Used as a placeholder for an illegible hanzi.