whistle (v.)
Old English hwistlian "to whistle," from Proto-Germanic *hwis-, of imitative origin (cognates: Old Norse hvisla "to whisper," Danish hvisle "to hiss;" see whisper (v.)). Used also in Middle English of the hissing of serpents; in 17c. it also could mean "whisper." Transitive use from late 15c. Related: Whistled; whistling. At public events, often an expression of support or encouragement in U.S., but often derisive in Britain. To whistle for (with small prospect of getting) is perhaps from nautical whistling for a wind, an old sailor's superstition during a calm. "Such men will not whistle during a storm" [Century Dictionary]. To whistle "Dixie" is from 1940.
whistle (n.)
"tubular musical instrument sounded by blowing," Old English hwistle (see whistle (v.)). Meaning "sound formed by pursing the lips and blowing" is from mid-15c. To wet one's whistle "take a drink" (late 14c.) originally may have referred to pipes, or be an allusion to the throat as a sort of pipe. Phrase clean as a whistle is recorded from 1878. Railroad whistle-stop (at which trains stop only if the engineer hears a signal from the station) is recorded from 1934.