Betwixt is an old-fashioned way of saying “between.” You might find it in older books, poems, or when someone wants to sound deliberately old-timey or playful.

Shakespeare used betwixt in his plays: “Betwixt mine eye and heart a league is took.” Today, we'd just say “between my eye and heart.” The phrase “betwixt and between” means stuck in the middle, unable to choose, or caught between two states. Someone might feel betwixt and between when they're too old for the little kids' table at Thanksgiving but not quite ready to sit with the adults.

While betwixt sounds quaint to modern ears, it works exactly like “between.” You can still use it if you want to add a medieval or poetic flavor to your writing, but in everyday conversation, “between” is the word people actually use. Think of betwixt as between's fancy, old-fashioned cousin who shows up at family reunions wearing a velvet cape.