Other forms: focused, focuses, focusing, focussed, focussing, foci
To focus is to make something sharp. You turn the ring on the lens until the face in the viewfinder stops being a blur — and you focus in the other way too, phone face down, door shut, one job in front of you.
As a noun, focus is the thing everybody is looking at: the focus of the meeting, the focus of the investigation. A photograph is in focus or out of focus, and a tired driver loses focus. The verb takes on and nothing else — you focus on a problem, you never focus at it. Spelling catches people out: focused and focusing with one s are standard now, though British books printed focussed for years. And the plural splits by trade — in maths and science an ellipse has two foci, while everywhere else it is focuses.
1verbconcentrateTo give all your attention to one thing.~28%
“Focus on the first three questions and leave the rest.”
synonyms: concentrate
2nouncentreThe thing that is getting all the attention.~44%
“Housing was the focus of the whole campaign.”
3verbfocusTo adjust a lens or your eyes until the image is sharp.~6%
“She focused the camera on the bird and waited.”
4nounstateThe state of being sharp and clear, in a picture or in a pair of eyes.~22%
“Half the photographs came out of focus.”
Shares are an estimate: a language model read 140 sentences found in the wild and placed 109 of them on a sense (31 were unclear) — a count of our sample, not a measurement of English.
Latin focus was the hearth — the fireplace, the burning middle of a Roman house. It had nothing to do with lenses until Kepler took it for the two points inside an ellipse: put a light at one focus and every ray it throws bounces off the curve and gathers at the other. That is why he chose the word, and the word kept the job. A focus is still the place where everything collects, and underneath it is still a fire.
Latin
focus — hearth, fireplace
English, today
focus
Latin focus (“hearth, fireplace”); see there for more. Related to fuel. Kepler introduced the term into mathematics and the sciences in describing elliptical orbits of planets (quote from Nicholas Mee): "One of the interesting properties of an ellipse is that if there were a light bulb at one focus, then all the light that it emits would reflect off the ellipse and converge at the other focus. This is why Kepler originally used the name focus for these points."
Etymology from Wiktionary, CC BY-SA