If you untie something that is tied to another thing or if you untie two things that are tied together, you remove the string or rope that holds them or that has been tied round them.

If you untie something such as string or rope, you undo it so that there is no knot or so that it is no longer tying something.

When you untie your shoelaces or your shoes, you loosen or undo the laces of your shoes.