When you disinherit someone, you decide not to leave that person anything in your will. Your eccentric grandfather might threaten to disinherit you because of your dirty fingernails.
You need to have written a will — a document that lists where you want your money and property to go after your death — in order to disinherit someone. When your wealthy relative actually removes your name from her will, she officially disinherits you. The word inherit is at the heart of disinherit, with its old-fashioned meaning, "make someone an heir." When you add the Latin prefix dis, "not," you take away the inheritance altogether.