Discretion
Etymology
From Latin discretio, "a separating, a distinguishing," from discernere, "to separate, to distinguish" ("dis-," apart, plus "cernere," to sift). The core idea is discernment — telling one thing from another. From "the power to tell things apart" the meaning grew into "sound judgment," and then into the specific tact of knowing what is best left unsaid.
noun · /dih-SKREH-shun/
Good judgment about what to say and do, especially the wisdom to keep confidences and avoid causing offense.
What it names
The trait of the person who knows what to withhold — trusted with secrets because they understand which truths not to broadcast.
Example
She handled the layoffs with such discretion that no one’s dignity was traded for office gossip.
Related idea
Tact is knowing how to say a difficult thing gracefully; discretion is knowing whether to say it at all.
noun · /dih-SKREH-shun/
The freedom or authority to decide and act as one sees fit.
What it names
delegated latitude — the power left to a person’s own judgment rather than fixed by rule
Example
Sentencing is left to the judge’s discretion within the legal limits.
Related idea
Here discretion is power, not tact; “at your discretion” hands over a choice, where prudence would guide how wisely to use it.