Do remember that clipart is an umbrella word for different types of non-photographic graphic images and that can include vector images 10 Amazing Sites to Find High-Quality Vector Art 10 Amazing Sites to Find High-Quality Vector Art Finding quality vector art for your designs can be time-consuming.
All images are under the CC0 license. Start with any of the 71, clip art images on this simple site.
Old Book Illustrations Old Book Illustrations offers a really nice collection of public domain illustrations scanned from old books and vector illustrations that can be modified and distributed for both personal and commercial projects.
New public domain images are added every weekday and everything on the site is available for commercial use read about their license here. Creative Commons is a set of licenses which automatically give you permission to do various things, such as reuse and distribute the content.
As new files are added daily, sort them by newest first. A new themes photo pack is release every Monday for purchase. It's one of many resources and you can still find clip art elsewhere.
All vector images can be dubbed as clip art, but not all clip art is made of vectors. As there are pros and cons to the argument, it all boils down to the purpose that is in front of you.