1. [n]  an electronic detector that scans automatically for some signal or condition; "they used scanners to monitor police radio channels"
2. [n]  a radar dish that rotates or oscillates in order to scan a broad area
3. [n]  an electronic device that generates a digital representation of a document for data input to a computer
4. [n]  someone who scans verse to determine the number and prosodic value of the syllables

1. An input device that takes in an optical image and digitises it into an electronic image represented as binary data. This can be used to create a computerised version of a photo or illustration.

A scanner may be linked to optical character recognition software allowing printed documents to be converted to electronic text without having to type them in at a keyboard.

2. lexical analyser.