a man who is polite and well educated, who has excellent manners and always behaves well

used to address or refer to a man, especially somebody you do not know

Ladies and gentlemen! Can I have your attention, please?

She was talking to an elderly gentleman.

used to address or refer to a male member of a legislature, for example the House of Representatives

a man from a high social class, especially one who does not need to work

He retired to his estate and lived the life of a country gentleman.

LEARNit Dictionary