1. Pertaining to the art of conducting international relations, as in negotiating alliances, treaties, and agreements: The diplomatic agent traveled to different countries and was successful in maintaining good rapport with other nations.
2. A reference to being tactful and skillful when dealing with people: While growing up, Jill learned that being diplomatic with her parents was quite effective in getting what she wanted, instead of her yelling and behaving badly!

Diplomatic applies to social behavior which is as sensitive as an ambassador's and so it applies to having social behavior that is smooth and courteous.

A reference to dining and diplomacy.

1. A container in which letters are sent between countries' representatives in other countries, and which is not examined by customs officials: Such a diplomatic bag can be a box, a duffel bag, a crate, a briefcase, etc., which has a lock, and may only contain items for official use only.
2. A bag in which official correspondence travels between a government office and an embassy of that government in another country, carried by a special messenger: The diplomatic bag is not subject to the same regulations that govern ordinary mail.

An official courier is also immune from detention or arrest, and he or she has the diplomatic bag under his protection and conveys it from one legal institution to another such authorized location of the same rulership in a different nation.

All of the ambassadors, ministers, etc. of foreign nations at the capital of a country: The diplomatic corps resides in a foreign country, is the collection of official heads of a mission, and represents their own nations and they get together at certain functions; such as, inaugurations, coronations, etc., depending on the local customs of the nation.

Special privileges that are accorded to diplomats and their families and staffs by international agreement: Diplomatic immunity includes freedom from arrest, searches, and taxations.