Indivisible means impossible to divide or separate into parts. The word combines “in-” (meaning “not”) with “divisible” (meaning “able to be divided”).

In mathematics, a number is indivisible by another number if you can't divide it evenly. The number 7 is indivisible by 2 because you can't split 7 into equal groups of 2 without having a remainder.

More broadly, indivisible describes things that must stay whole to work properly or keep their meaning. A strong friendship might feel indivisible, meaning nothing could break it apart. When the Pledge of Allegiance calls America “one nation, indivisible,” it expresses the idea that the country should remain united and whole, not split into separate pieces.

Some things are physically indivisible: atoms were once thought to be the smallest, indivisible units of matter (though scientists later discovered that even atoms have parts). Other things are indivisible by principle or necessity: some people argue that certain rights are indivisible from being human, meaning they can't be separated from a person's basic dignity.