/bəˈrɒmɪtər/
[noun] An instrument used to measure air pressure, which helps predict changes in the weather. It is also used more broadly to describe anything that shows or measures how a situation is changing.
The word 'barometer' was invented at almost the exact same moment as the instrument itself — coined by the scientist who built the first one.
The story of 'barometer' begins in ancient Greek, with two words that described very physical, tangible things. The first is 'baros' (βάρος), meaning 'weight' or 'heaviness'. The second is 'metron' (μέτρον), meaning 'measure'. Together, these two roots perfectly describe what the instrument does: it measures the weight — or pressure — of the air pressing down on us from above. Greek 'baros' itself comes from an even older Proto-Indo-European root, '*gwer-', which carried the sense of heaviness, and which also gave us the Latin 'gravis', meaning heavy, which then passed through Old French as 'grave' into English words like 'gravity' and 'grave' (meaning serious).
The instrument itself was invented in 1643 by the Italian physicist Evangelista Torricelli, a student of Galileo. Torricelli discovered that the atmosphere exerts pressure by filling a glass tube with mercury and observing how the liquid rose and fell depending on conditions. He did not name his invention, but the scientific community quickly needed a word for it. The term 'barometer' was coined — most likely by the English scientist Robert Boyle — around 1665, drawing directly from the Greek roots 'baros' and 'metron' to create a single, elegant scientific Latin compound: 'barometrum'. From there it entered English almost immediately as 'barometer'.
This pattern of building scientific vocabulary from Greek roots was extremely common in the 17th century. As the Scientific Revolution swept through Europe, scholars across different countries needed shared, neutral vocabulary that did not belong to any one spoken language. Greek and Latin provided that neutral ground. Dozens of new instruments were named this way during this period — 'thermometer' (from Greek 'thermos', heat, and 'metron'), 'hygrometer' (from Greek 'hygros', wet), and many others followed the same recipe. 'Barometer' was part of this great wave of scientific naming.
By the early 18th century, the barometer was a common fixture in English homes and ships, and the word was firmly established in everyday speech. But something interesting then happened to its meaning. Because the barometer was so reliably used to predict what was coming — good weather or bad — people began using the word in a broader, figurative sense. A politician's approval rating became a 'barometer of public opinion'. Share prices became a 'barometer of economic confidence'. The word stretched from the physical to the abstract, measuring not air pressure but social mood, cultural change, or political climate.
This figurative expansion is entirely logical, and it shows how a very precise technical word can become a rich metaphor over time. Today, 'barometer' lives comfortably in both worlds. A scientist uses it to describe an instrument with mercury or an aneroid capsule; a journalist uses it to describe a telling sign of how society feels about something. The word's journey — from Greek philosophy, through Italian physics, into English drawing rooms, and finally into everyday metaphor — is a small but perfect example of how language and discovery travel together.