1. noun A very devoted subset of group or organization. They're the hard core of the group, so I'd talk them if you're interested in volunteering.

2. noun A style of rock music that is especially loud and aggressive. Usually spelled as one word. I used to listen to hardcore, but I've moved on to other genres.

3. adjective Describing someone who is staunch and unyielding in their beliefs. Often hyphenated or spelled as one word. She's a hard-core liberal, so good luck getting her to listen to your conservative views.

4. adjective Describing pornography that is especially graphic or explicit. Often hyphenated or spelled as one word. I was appalled to find hard-core porn on his computer.

5. adjective Describing something that is especially intense or impressive. Often hyphenated or spelled as one word. Wow, you're really specializing in surgery? That's hardcore!

6. adjective Describing a style of rock music that is especially loud and aggressive. Usually spelled as one word. I used to play in a hardcore punk band back in college.