1. either of two children or animals brought forth at a birth.
2. either of two persons or things closely related to or closely resembling each other.
3. twin bed.
4. twins, Astronomy, Astrology. The constellation or sign of Gemini.
5. being a twin or twins: twin sisters.
6. being one of a pair; identical: a twin bracelet; a twin peak.
7. to bring together in close relationship; pair; couple.
8. informal, to divide or convert into two, parts, similar items, etc.