Beginning of every Washington State ZIP code

NINE

Think of the first digit shared by all ZIP codes in the Evergreen State, which also happens to be the highest single-digit number.

Washington State ZIP codes all start with the number 9, like 98001 for Seattle or 99201 for Spokane. The clue plays on "beginning" meaning the first digit, and "every" confirms it applies to all ZIP codes in the state. Since "nine" is how you spell out that digit, the answer is "NINE" instead of just the number 9.