The largest font style available in Microsoft Word is called "Heading 1", and it has a font size of 22 point. It is typically used for titles and headings. Other large sizes are available, such as 18-point for subtitles, 16-point for subheadings, 14-point for body text, and 12-point for footnotes. You can also create your own custom font size by entering the desired point size in the Font Size box on the Home tab of the ribbon.
When using large fonts, it is important to keep readability in mind. Large fonts are great for adding emphasis, but if they are too big and overwhelming they can make text hard to read. For best results, try to use no more than three different font sizes on a single page. Also, make sure that the text contrast and spacing are suitable for easy reading.
Remember, your main goal is to create effective communication with your audience — so choose font styles and sizes that make sense for your content!