Steam whistle Meaning, Definition & Usage

  1. noun a whistle in which the sound is produced by steam; usually attached to a steam boiler

WordNet

Definitions
  1. an apparatus attached to a steam boiler, as of a locomotive, through which steam is rapidly discharged, producing a loud whistle which serves as a warning signal. The steam issues from a narrow annular orifice around the upper edge of the lower cup or hemisphere, striking the thin edge of the bell above it, and producing sound in the manner of an organ pipe or a common whistle.

Webster 1913