What it means, in its simplest terms, is that she thinks before she speaks. How often have we been guilty of the opposite, of speaking before we think? How often have we said something (a quick comment, a small mean remark) and wished we could take it back? The wise person has learned that nothing which is ever said can be "taken back" effectively.
A woman who opens her mouth in wisdom is not, thereby, "repressing" herself. She is disciplining herself. She has learned that her husband (and children and everyone else) has feelings, too, and that a concern for their feelings is wise and godly concern.
This is hardest for those who were raised by people who were not wise in their language. Many parents (too many parents) simply dump whatever they are thinking on their children. Many women were raised by mothers who did not control their words at all, but were hurtful. Many fathers were harsh and unfair, even cruel and cutting. We all know the things that were said in our youth.
But you may not realize how much what happened in your youth has affected how you interact with your family. There are women (and men) whose language in the home is cold and, yes, cruel. They insult out of habit, not out of evil. They have learned (from their experience as children) that a wife can be abused and must "stand up for herself," and they do not realize that their husband is not like their father.
You've seen them. At the mall, at restaurants, at public events, all the parents whose children are learning the same lessons of bitterness and cutting remarks. There are people whose tone of voice communicates hatred, even though they do not hate. There are people whose choice of words is bitter, although they are not bitter. You can recognize them when the husband or child reacts to their display of anger, and they respond with "no, I'm not mad." But they acted mad.
You hear it in the cursing used in commonplace conversations between parents and children. You see it in the way they grab their children and jerk them around. You see it in little asides and cutting comments. You see its results in the way the children react to their parents and the way the parents react to each other. Sometimes, it has become so much a part of who they are that they seem to be unaware of the horror with which everyone views them.
The excellent wife knows that her words are of tremendous importance in the home. She can be a great source of good, of peace, of a loving home. Or she can be the source of bitterness, hurt feelings, and a desire to escape.
How do you open your mouth in your home? In wisdom? Or in carelessness and self-deception? An excellent wife opens her mouth in wisdom, and her family is warmed and nourished by her words.