na-adjective, noun
Describes a person who speaks smoothly and persuasively, often with a nuance of being a smooth talker. Can be used positively or with slight suspicion.
彼は口巧者で、どんな相手ともすぐに打ち解ける。
He is smooth-spoken and quickly gets along with anyone.
口巧者なセールスマンに気をつけて。
Be careful of glib salespeople.
雄弁 means 'eloquence' and is more formal, often used for public speaking rather than casual smooth talk.
Compound of 口 (mouth, speech) and 巧者 (skillful person). The exact historical derivation is uncertain, but the word literally suggests a person skilled with words.