A shy person is nervous and uncomfortable in the company of other people.

If you are shy of doing something, you are unwilling to do it because you are afraid of what might happen.

When a horse shies, it moves away suddenly, because something has frightened it.

You say 'once bitten, twice shy' when you want to indicate that someone will not do something a second time because they had a bad experience the first time they did it.

If you fight shy of something, you try very hard to avoid it.

A number or amount that is just shy of another number or amount is just under it.