hwistlian

Whistle comes from Old English hwistlian, an onomatopoeic verb — the word sounds like the action it describes. The Proto-Germanic root was *hwistlōną, also imitative. The initial hw- cluster, which Old English spelled as 'hw-' but which is now spelled 'wh-', reflected an actual consonant sound — a voiceless labio-velar approximant, /ʍ/, like saying 'w' while blowing air. Some English dialects still pronounce the /ʍ/ in whistle, which, and whether.

The noun whistle — an instrument that produces a whistling sound — appeared in Old English as hwistle. It referred to a simple tube that produced a tone when air was blown through it. Whistles made of bone and wood have been found at archaeological sites dating to the Neolithic. The earliest known musical instrument of any kind — a bone flute found at Divje Babe in Slovenia — dates to approximately 60,000 years ago. Whistling may be older than language itself.

The word expanded into idioms and compounds that have lasted centuries. To 'wet your whistle' means to have a drink (the whistle is your throat). To 'blow the whistle' on someone means to expose wrongdoing (from the referee's whistle stopping play). 'Whistleblower' — the compound noun — was coined in the 1970s for someone who reports institutional wrongdoing. Ralph Nader is credited with popularizing the term.

The word's stability is remarkable. Unlike most English words, which have been borrowed, replaced, or radically reshaped since Old English, whistle has remained essentially unchanged for over a thousand years. The sound it imitates has not changed. The action it describes has not changed. The word had no reason to change either.