Something that is nasty is very unpleasant to see, experience, or feel.

If you describe a person or their behaviour as nasty, you mean that they behave in an unkind and unpleasant way.

If you describe something as nasty, you mean it is unattractive, undesirable, or in bad taste.

A nasty problem or situation is very worrying and difficult to deal with.

If you describe an injury or a disease as nasty, you mean that it is serious or looks unpleasant.

Nasties are unpleasant or harmful people or things.