To force category names to stay on one line in drop-down menus, you can adjust the CSS of your website. Typically, you'll want to set a white-space property to nowrap in the CSS for the menu items, preventing the text from wrapping onto a second line. You may also need to adjust the width or padding of the drop-down menu to ensure there's enough space for longer category names. Here's an example CSS snippet:

.dropdown-menu li a {
    white-space: nowrap;
}
This will ensure the category names remain on a single line in your menu.