A sharp tongue is the only edge tool that grows keener with constant use.

A tart temper never mellows with age, and a sharp tongue is the only edged tool that grows keener with constant use.

The tongue is the only tool that gets sharper with use

The tongue is the only tool that gets sharper with use.

The tongue deviseth mischiefs; like a sharp razor, working deceitfully.

He nothing common did, or mean, / Upon that memorable scene, / But with his keener eye / The axe's edge did try.