The most suitable one word substitute for the given expression "a person who is talkative" is garrulous.

• Orator is a person who is skilled in public speaking.
• Gregarious is a person who enjoys being around other people.
• Speaker is a person who speaks publicly.

Garrulous means "given to excessive talking." It is a more informal word than "talkative," and it often has a negative connotation. A garrulous person may talk too much, and they may not be very good at listening to others.