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

Scanner
from Bluestar

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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.