focus

UK: /ˈfəʊkəs/ US: /ˈfoʊkəs/ ,(fō′kəs)

Inflections of 'focus' (n):

focuses

npl

foci

npl

Inflections of 'focus' (v): (⇒ conjugate)

Spellings with a double "s" are mainly used in UK English. They are correct in US English, but rare.

focuses

v 3rd person singular (US & UK)

focusses

v 3rd person singular (Mainly UK)

focusing

v pres p (US & UK)

focussing

v pres p (Mainly UK)

focused

v past (US & UK)

focussed

v past (Mainly UK)

focused

v past p (US & UK)

focussed

v past p (Mainly UK)

WordReference Random House Learner's Dictionary of American English © 2025

fo•cus /ˈfoʊkəs/   n., pl. -cus•es, -ci /-saɪ, -kaɪ/   v., -cused, -cus•ing or (esp. Brit.) -cussed, -cus•sing. 

n. 

1. a central point, such as of attraction, attention, or activity:
   [countable] His focus was on earning a living.
2. Physics [countable] a point at which rays of light, heat, or other radiation meet after being refracted or reflected.
3. Optics the adjustment of an optical device that is necessary to produce a clear image:
   [uncountable] The image is in focus.

v. 

4. to (cause to) come to a focus or into focus: [~ + object]
   to focus the lens of a camera.
   [no object]
   For a few moments my eyes wouldn't focus.
5. to concentrate: [~ + object]
   I tried to focus my thoughts.
   [no object* (~ + on + object)]
   I tried to focus on the project.

WordReference Random House Unabridged Dictionary of American English © 2025

fo•cus  (fō′kəs), n., pl. -cus•es, -ci (-sī, -kī),  v., -cused, -cus•ing or (esp. Brit.) -cussed, -cus•sing. 

n. 

1. a central point, as of attraction, attention, or activity:
   The need to prevent a nuclear war became the focus of all diplomatic efforts.
2. Physics a point at which rays of light, heat, or other radiation, meet after being refracted or reflected.
3. Optics
   • the focal point of a lens.
   • the focal length of a lens.
   • the clear and sharply defined condition of an image.
   • the position of a viewed object or the adjustment of an optical device necessary to produce a clear image:
     in focus; out of focus.
4. Mathematics [Geom.] (of a conic section) a point having the property that the distances from any point on a curve to it and to a fixed line have a constant ratio for all points on the curve. See diag. under ellipse, hyperbola, parabola. 
5. Geology the point of origin of an earthquake.
6. [Pathol.] the primary center from which a disease develops or in which it localizes.

v.t. 

7. to bring to a focus or into focus:
   to focus the lens of a camera.
8. to concentrate:
   to focus one's thoughts.

v.i. 

9. to become focused.

• Latin: fireplace, hearth
• 1635–45

fo′cus•a•ble, adj. 
fo′cus•er, n. 
Synonyms

• 1. center, heart, core, nucleus.

Collins Concise English Dictionary © HarperCollins Publishers::

focus / ˈfəʊkəs/ noun ( -cuses, -ci / -saɪ -kaɪ -kiː/)

1. a point of convergence of light or other electromagnetic radiation, particles, sound waves, etc, or a point from which they appear to diverge
2. another name for focal point1, focal length
3. the state of an optical image when it is distinct and clearly defined or the state of an instrument producing this image: the picture is in focus, the telescope is out of focus
4. a point upon which attention, activity, etc, is directed or concentrated
5. a fixed reference point on the concave side of a conic section, used when defining its eccentricity
6. the point beneath the earth's surface at which an earthquake or underground nuclear explosion originates
   Compare epicentre
7. the main site of an infection or a localized region of diseased tissue

verb ( -cuses, -cusing, -cused, -cusses, -cussing, -cussed)

1. to bring or come to a focus or into focus
2. (transitive) often followed by on: to fix attention (on); concentrate

Etymology: 17th Century: via New Latin from Latin: hearth, fireplace

ˈfocuser noun