eloquent tongue; silver tongue
Idiomatic expression referring to a persuasive or eloquent speaker. Literally 'a three-inch tongue', it emphasizes that a small tongue can have great power.
彼は三寸の舌で大勢の人を説得した。
He persuaded many people with his eloquent tongue.
From Chinese 三寸之舌 “a three-inch tongue,” an ancient metaphor for eloquent speech and its power to influence others.