I think modesty is action and posture, and humility is a state of being (maybe a biochemical or emotional state, at some level). After writing that last week, I found this on Tuesday/yesterday:

Humility is an essential attitude for success in the spiritual life. Any self-conceit, whether nurtured by superior intelligence, wealth, a high position, or the praise of others, is an obstacle on the path. Genuine humility is not posturing.

(from intro to "humility" on unification.net)

Confucius said, "A gentleman does not grieve that people do not recognize his merits; he grieves at his own incapacities."

Confucianism. Analects 14.32

To know when one does not know is best. To think one knows when one does not know is a dire disease.

Taoism. Tao Te Ching 71

The fool who knows that he is a fool is for that very reason a wise man; the fool who thinks he is wise is called a fool indeed.

Buddhism. Dhammapada 63

Do nothing from selfishness or conceit, but in humility count others better than yourselves.

Christianity. Philippians 2.3

Opposite seems "arrogance" but there are other terms to consider in and around "humility" and "modesty." Confidence. Self-assuredness. Confidence can be confidence both in what you can do and what you can't. That comes back to truth and reliability.

Practice Humility

Humility and inner peace go hand in hand. The less compelled you are to try to prove yourself to others, the easier it is to feel peaceful inside.

Proving yourself is a dangerous trap. It takes an enormous amount of energy to be continually pointing out your accomplishments, bragging, or trying to convince others of your worth as a human being. Bragging actually dilutes the positive feelings you receive from an accomplishment or something you are proud of. To make matters worse, the more you try to prove yourself, the more others will avoid you, talk behind your back about your insecure need to brag, and perhaps even resent you.

Ironically, however, the less you care about seeking approval, the more approval you seem to get. People are drawn to those with a quiet, inner confidence, people who don't need to make themselves look good, be ?"right"? all the time, or steal the glory. Most people love a person who doesn't need to brag, a person who shares from his or her heart and not from his or her ego.

The way to develop genuine humility is to practice. It's nice because you will get immediate inner feedback in the way of calm, easy feelings. The next time you have an opportunity to brag, resist the temptation. I discussed this strategy with a client, and he shared the following story: He was with a group of friends a few days after he had been promoted at work. His friends didn't know it yet, but my client was chosen to be promoted instead of another friend of theirs. He was a little competitive with this person, and had the very strong temptation to sneak in the fact that he had been chosen and their other friend wasn't. He felt himself about ready to say something, when a little voice inside him said, "Stop. Don't do it!" He went ahead and shared with his friends, but didn't cross the line and turn the sharing into gloating. He never mentioned how their other friend didn't get promoted. He told me that he couldn't remember ever feeling so calm and proud of himself. He was able to enjoy his success without bragging. Later, when his friends did find out what had happened, they let him now that they were extremely impressed with his good judgment and humility. He received more positive feedback and attention from practicing humility—not less.