1.Definition: (of information) given in confidence or in secret
"This arrangement must be kept confidential"
2.Definition: denoting confidence or intimacy
"A confidential approach", "In confidential tone of voice"
3.Definition: entrusted with private information and the confidence of another
"A confidential secretary"
4.Definition: the level of official classification for documents next above restricted and below secret; available only to persons authorized to see documents so classified