- (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.
- Antonym: ○
- (logic) logically necessary; provable
- (astrology) quadrature.
- (alchemy) salt.
- See ☐ for a blank ballot.
- (logical necessity): ◊
- Used as a placeholder for an illegible hanzi or lacuna.
- Used as a placeholder for an unknown hanzi (as when discussing dialectal morphemes).
- (Internet slang) Used in self-censorship of sensitive characters.
- alt. forms: 口 (kǒu)