Other forms: silver tongues
Having a silver tongue means being a clever, persuasive speaker. A car salesperson with a silver tongue can convince customers that they desperately need the fanciest SUV on the lot.
People with silver tongues have a way with words, an eloquent style of speaking. This term is often used for those who use their gift of gab in a sneaky or deceptive way, influencing others to do what they want. Somehow, your sister's silver tongue always seems to get her that last cookie or a ride in the front seat. This 16th-century idiom comes from an obscure meaning of silver, "melodious or pleasantly resonant."