One who observes, or pays attention to, anything; especially, one engaged in, or trained to habits of, close and exact observation; as, an astronomical observer.
- One that observes: an observer of local customs; observers of religious holidays.
- A delegate sent to observe and report on the proceedings of an assembly or a meeting but not vote or otherwise participate.
- A crew member on a military aircraft who makes observations.
- A member of an armed force who watches and reports from an observation post.