focus

Borrowed from Latin focus (“hearth, fireplace”); see there for more.

• (UK) IPA^(key): /ˈfəʊ.kəs/
• (US) IPA^(key): /ˈfoʊ.kəs/
• Rhymes: -əʊkəs

focus (countable and uncountable, plural foci or focuses)

1. (countable, optics) A point at which reflected or refracted rays of light converge.

   The heat of sunlight at the focus of a magnifying glass can easily set dry leaves on fire.

2. (countable, geometry) A point of a conic at which rays reflected from a curve or surface converge.
3. (uncountable, photography, cinematography) The fact of the convergence of light on the photographic medium.
   • 2013 July-August, Catherine Clabby, “Focus on Everything”, in American Scientist:

     Not long ago, it was difficult to produce photographs of tiny creatures with every part in focus. […] A photo processing technique called focus stacking has changed that. Developed as a tool to electronically combine the sharpest bits of multiple digital images, focus stacking is a boon to biologists seeking full focus on a micron scale.

   Unfortunately, the license plate is out of focus in this image.

4. (uncountable, photography, cinematography) The quality of the convergence of light on the photographic medium.

   During this scene, the boy’s face shifts subtly from soft focus into sharp focus.

5. (uncountable) Concentration of attention.

   I believe I can bring the high degree of focus required for this important job.

6. (countable, seismology) The exact point of where an earthquake occurs, in three dimensions (underneath the epicentre).

   The earthquake's focus was at exactly 37 degrees north, 18 degrees south, seventy five meters below the ground.

7. (computing, graphical user interface) The indicator of the currently active element in a user interface.

   Text entered at the keyboard or pasted from a clipboard is sent to the component which currently has the focus.

8. (linguistics) The most important word or phrase in a sentence or passage, or the one that imparts information.

• focus hunting

focus (third-person singular simple present focuses or focusses, present participle focusing or focussing, simple past and past participle focused or focussed)

1. (transitive) To cause (rays of light, etc) to converge at a single point.
2. (transitive) To adjust (a lens, an optical instrument) in order to position an image with respect to the focal plane.

   You'll need to focus the microscope carefully in order to capture the full detail of this surface.

3. (transitive, followed by on or upon) To concentrate one's attention.

   Focus on passing the test.

4. (intransitive) To concentrate one’s attention.

   If you're going to beat your competitors, you need to focus.

5. (computing, graphical user interface, transitive) To transfer the input focus to (a visual element), so that it receives subsequent input.

   The text box won't receive the user's keystrokes unless you explicitly focus it.

The spellings focusses, focussing, focussed are more common in Commonwealth English than in American English, but in both varieties they are less common than the spellings focuses, focusing, focused.

• focus group
• in focus
• out of focus
• soft focus

• focal

• Fusco

Borrowed from Latin focus. Compare the inherited doublet foc.

• (Balearic, Central, Valencian) IPA^(key): /ˈfɔ.kus/

focus m (plural focus)

1. focus

Borrowed from Latin focus, whence also Italian fuoco (an inherited doublet).

• IPA^(key): /ˈfɔkus/, [ˈfɔː.kus̪]
• Hyphenation: fò‧cus

focus m (invariable)

1. focus (all senses)

• The origin is uncertain. Usually connected with Old Armenian բոց (bocʿ).
• Some connect this along with faciēs, facētus, fax, from Proto-Indo-European *bʰeh₂- (“to shine”). Cognate with Ancient Greek φαίνω (phaínō, “to shine”).
• In explaining how Kepler discovered the elliptical orbits, Nicholas Mee provides this explanation:

"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." (Gravity, 2014, p. 74)

• (Classical) IPA^(key): /ˈfo.kus/, [ˈfɔ.kʊs]
• (Ecclesiastical) IPA^(key): /ˈfo.kus/, [ˈfoː.kus]

focus m (genitive focī); second declension

1. fireplace, hearth
2. firepan, coal pan, brazier
3. (figuratively) house, family
4. (Vulgar Latin) fire

Second-declension noun.

• focillare
• foculare

• focus in Charlton T. Lewis and Charles Short (1879) A Latin Dictionary, Oxford: Clarendon Press
• focus in Charlton T. Lewis (1891) An Elementary Latin Dictionary, New York: Harper & Brothers
• focus in Charles du Fresne du Cange’s Glossarium Mediæ et Infimæ Latinitatis (augmented edition, 1883–1887)
• focus in Gaffiot, Félix (1934) Dictionnaire Illustré Latin-Français, Hachette
• Carl Meissner; Henry William Auden (1894) Latin Phrase-Book‎, London: Macmillan and Co.
  • to fight for hearth and home: pro aris et focis pugnare, certare, dimicare
    
• focus in Harry Thurston Peck, editor (1898) Harper's Dictionary of Classical Antiquities, New York: Harper & Brothers
• focus in William Smith et al., editor (1890) A Dictionary of Greek and Roman Antiquities, London: William Wayte. G. E. Marindin