Noun

1. A flag or standard used by a military commander, monarch or nation.
2. Any large sign, especially if constructed of soft material or fabric.

   The mayor hung a banner across Main Street to commemorate the town's 100th anniversary.

3. A large piece of silk or other cloth, with a device or motto, extended on a crosspiece, and borne in a procession, or suspended in some conspicuous place.
4. By extension, a cause or purpose; a campaign or movement.

   They usually make their case under the banner of environmentalism.

5. The title of a newspaper as printed on its front page; the nameplate; masthead.
6. A type of advertisement in a web page or on television, usually taking the form of a graphic or animation above or alongside the content. Contrast popup, interstitial.
7. The principal standard of a knight.
8. A person etc. who bans something.

Adjective

1. Exceptional; very good.

   It is a banner achievement for an athlete to run a mile in under four minutes.