noun

horn

An informal term for a telephone.

He gets his colleague on the horn.

Etymology

Horn already named a sound-producing or sound-projecting device. Telephone slang transfers that familiar instrument name to a device used for transmitting speech.

More examples

She spent an hour on the horn with the supplier.
The character tells him to pick up the horn.
The old dialogue uses horn for telephone.

Forms

horn · horns

Similar words

phone: The usual everyday word.
telephone: The full neutral term.