Reader (noun)

1. A person who reads, especially one who reads a particular type of text.
2. A device or machine used for reading, typically a book or magazine.
3. A person who reads a book or other text aloud.
4. A person who reads a specific subject or profession.
5. An indicator or gauge used to measure or display a specific value.

Origin:

Late middle english: from old french, from lire "read".

Examples:

1. He is an avid reader.
2. He was reading a book on his e-reader.
3. The reader read the story to the children.
4. The reader is a specialist in medieval literature.
5. The fuel gauge is a reader of the fuel level.