The prefix inter- means “between” or “among.” When you see inter- at the start of a word, it signals that something involves two or more things connecting, crossing, or existing in the space between them.

An international flight travels between nations. An interstate highway connects different states. When you interrupt someone, you break into the space between their words. An intermission is the break between acts of a play.

Sometimes inter- suggests things working together: interaction means people or things acting with each other, and interdependent describes how different parts rely on one another. A coral reef is interdependent because the fish, coral, and other creatures all need each other to survive.

Other times it emphasizes the between-ness itself: an interval is the time between events, like the interval between lunch and recess. Interstellar space is the vast emptiness between stars.

You'll find inter- everywhere once you start looking: intercept, intermediate, interlocking. Each time, think about what's between or among. Understanding this prefix unlocks dozens of words at once.