Please tell Lord Nobunaga.
The kanji and the word are exactly the same. That means they share meanings as well. This is put on people's names, though most likely you'll only see this when someone is being sarcastic or if you're watching a samurai TV show. "おはようございます！こういち殿！"
Since this word is made up of a single kanji, it probably uses the kun'yomi reading. You did not learn this reading, so here's a mnemonic to help you to remember: Who is your great lord? Imagine it being someone named Don (どの). If you know a Don, that's great, imagine that person. If you don't, think of a famous Don that's out there.