/maʊs/
[noun] A small rodent with a pointed nose, large ears, and a long tail, often found in homes and fields. The word also refers to the small hand-held device used to control a computer cursor.
The word 'mouse' has barely changed in over 3,000 years — ancient Indo-European speakers would almost recognise it today.
Few English words carry as much unbroken history as 'mouse.' Its roots reach back to Proto-Indo-European, the ancient ancestor language spoken roughly 5,000 to 6,000 years ago, where the reconstructed word *mūs referred to the small, scurrying rodent we still recognise instantly. This makes 'mouse' one of the oldest continuously surviving words in the English language, changed in sound but barely changed in spirit across dozens of centuries and dozens of cultures.
From Proto-Indo-European *mūs, the word spread outward in almost every direction. Ancient Greeks called the animal mys (μῦς), and from this same root their word for muscle — mys — was born, because the shape of a flexing muscle under skin reminded them of a little mouse moving beneath cloth. That Greek connection gave the world 'muscle,' tracing its path as Greek mys → Latin musculus (meaning both 'little mouse' and 'muscle') → Old French muscle → Middle English muscle. Latin also preserved the original animal word directly: Latin mūs was used by Roman writers to describe the creature itself, and it branched into old scientific vocabulary that still populates biology today.
In Old English, the word arrived as mūs, essentially the same sound the Proto-Indo-European speakers had used millennia earlier. Old English mūs produced a plural by changing the vowel — mȳs — which is exactly how the modern plural 'mice' was formed. This kind of internal vowel change, called an umlaut, is the same process that gives English 'foot' and 'feet,' or 'goose' and 'geese.' It is a piece of living grammar from an age before writing.
The word sailed through Middle English largely intact, shifting in pronunciation as the Great Vowel Shift of the 14th to 17th centuries moved long vowels around English speech. The Middle English form was mous, and by the time English spelling became more standardised in the 16th and 17th centuries, 'mouse' settled into the form we know today. During all this time, its meaning was utterly stable — it meant exactly the same small creature it had always meant.
The great modern twist in the word's life came in 1965, when American computer engineer Douglas Engelbart invented the hand-held pointing device at Stanford Research Institute and needed a name for it. The small, rounded device with its trailing wire looked — to Engelbart and his colleagues — exactly like a mouse with a tail. The name was informal at first, almost a joke among engineers, but it spread through research labs, into early personal computers, and finally into every home on earth. In an extraordinary piece of linguistic history, a word over 5,000 years old simply expanded its meaning to cover one of the most modern objects in human experience. The ancient farmers who first named this creature could never have imagined it — but the metaphor they would have understood perfectly.