WP appending -2 to the end of my slug. Where are the originals stored so I can delete them?

I’ve been learning about taxonomies, custom posts etc though a lot of trial and error. I finally have it working how I want, however now I am getting some conflict with my desired slugs. I can’t name my category “venue” because someplace in the database, that’s already taken (I assume) – even though I’ve deleted the category that used it. Now when I try adding the category that I want to use the “venue” slug, WP automatically makes it “venue-2”, which I definitely don’t want in my url as the folder. Any suggestions for this?

This can also be caused by uploading images with the same file name as the post/page. In my case, I uploaded an image called ‘careers.jpg’ before I created a page called ‘Careers’, so the page was getting the ‘-2’ appended. To fix it, I just changed the slug on the image, then I was able to change the slug on the page.