A conversationalist is someone who is good at talk — not just chatting about the weather, but keeping a conversation alive with interesting, funny, or thoughtful things. You praise a person by calling them a good conversationalist. It is a complimentary word, a little educated or old-fashioned. You might use it about a dinner guest, or in a book. Teenagers almost never say it; they might say someone is good to talk to, or funny. Talking a lot is not the same thing. A person who never stops, but says nothing worth hearing, is not a conversationalist. The skill is conversation; the person who has it is the conversationalist.