To make a promise.

Synonym of good as one's word

Do what one has said one will do.

To promise.

To break a promise one has made.

(figuratively) to think carefully about what one will say.

To be forced to retract a prior statement after it has been shown to be disproven; to take back what one has said. / To speak at a low volume due to uncertainty about one's speech; to mumble.