To attempt to persuade someone about (something) through understatement, so that the listener accepts the good points as obvious.
To reduce the force or impact of (something); to damp, to mute; especially, to minimize the less desirable aspects of (something); to play down, to tone down.
To reduce the volume of (music, a sound, etc.).
Chiefly followed by on: to act in a less assertive or forceful manner.