1. mod. sexually explicit; pornographic. You can’t sell that hard-core stuff in a store like this!
2. mod. extreme; entrenched. There are too many hard-core cases of poverty there.
3. mod. very good; stunning; great. I’d like a really hard-core pizza with at least five kinds of cheese.
4. mod. extreme; quintessential. She thinks of herself as a hard-core leftist.