[ foh-kuhs ]
/ ˈfoʊ kəs /

noun, plural fo·cus·es, fo·ci [foh-sahy, -kahy] /ˈfoʊ saɪ, -kaɪ/.

verb (used with object), fo·cused, fo·cus·ing or (especially British) fo·cussed, fo·cus·sing.

to bring to a focus or into focus; cause to converge on a perceived point: to focus the lens of a camera.
to concentrate: to focus one's thoughts; to focus troop deployment in the east.

verb (used without object), fo·cused, fo·cus·ing or (especially British) fo·cussed, fo·cus·sing.

to be or become focused: My eyes have trouble focusing on distant objects.
to direct one's attention or efforts: Students must focus in class.

Origin of focus

1635–45; < Latin: fireplace, hearth



Where does focus come from?

What does the word focus bring to your mind? Maybe you think of a photograph that is clear and sharply defined. Or perhaps you recall a teacher tsk-tsking you to pay attention in class. But what about a fireplace?

Well, the word focus comes directly from the Latin focus, which meant “fireplace” or “hearth” (that is, the floor of a fireplace). This is what focus originally meant in English when the word entered the language around 1635–45, though that sense has been extinguished, as it were.

But the word focus burned on in other ways. As the 1600s unfolded, focus was given new meanings in the great scientific literature of that age, which were largely written in what’s known as New Latin. In the 1650s, the influential English philosopher and author Thomas Hobbes used focus for a kind of fixed point in geometry. So did Isaac Newton—you know, of gravity fame—in the 1690s.

Other applications of the word focus in the late 1600s came about in the fields of medicine and physics. In physics, a focus is “a point at which rays of light, heat, or other radiation meet after being refracted or reflected.” Perhaps you can imagine how a fireplace or a hearth—contained areas and sources of heat and light—was likened to such a point in math and science.

Dig deeper

The word focus took on a number of senses in optics, specifically “the point on a lens on which rays converge or from which they deviate.” A more familiar sense of focus is “the clear and sharply defined condition of an image,” as when the image isn’t blurry. Optics has also given us the expressions in focus and out of focus, which can be used both literally and figuratively.

From these various ideas of clarity and convergence in optics arises one of the more common, everyday ways we use the word focus today: “a central point, as a of attention, activity, or activity.” For example, Finding a cure for cancer was the focus of his long career. Focus also refers to ability to concentrate, as in The teacher felt the students struggled with their focus. These senses of focus had spread by the early 1800s, around when various verb forms of focus take off. The adjective form of focus is focal.

Did you know ... ?

The Latin word focus became the general word for “fire” in the language’s descendants. Spanish fuego, French fue, Italian fuoco, Portuguese fogo, Romanian foco, to cite just the most spoken Romance languages—all of these words for “fire” come from the Latin focus.

So does another French word for a different part of the house: the foyer. A foyer refers to a lobby of a theater, hotel, or apartment house. In French, a foyer was originally a room to which theater audiences went for warmth between the acts.

There’s just something about a fireplace, isn’t there? Its magic wasn’t lost on the ancient Romans, either: focus was also extended to mean “home, family,” a metaphor also at work in English’s very own word hearth. Now that warms the heart, doesn’t it?

Example sentences from the Web for focus

British Dictionary definitions for focus

/ (ˈfəʊkəs) /

noun plural -cuses or -ci (-saɪ, -kaɪ, -kiː)

verb -cuses, -cusing, -cused, -cusses, -cussing or -cussed

to bring or come to a focus or into focus
(tr often foll by on) to fix attention (on); concentrate

Derived forms of focus

focusable, adjective focuser, noun

Word Origin for focus

C17: via New Latin from Latin: hearth, fireplace

Medical definitions for focus

[ fōkəs ]

n. pl. fo•cus•es


Scientific definitions for focus

[ fōkəs ]

Plural focuses or foci (sī′, fōkī′)

The degree of clarity with which an eye or optical instrument produces an image.
See focal point.
A central point or region, such as the point at which an earthquake starts.
Mathematics A fixed point or one of a pair of fixed points used in generating a curve such as an ellipse, parabola, or hyperbola.
The region of a localized bodily infection or disease.