diffusion

noun

dif·​fu·​sion di-ˈfyü-zhən 

plural diffusions

1

: the state of being spread out or transmitted especially by contact : the action of diffusing

the diffusion of knowledge/ideas/technology

2

: prolixity, diffuseness

3

a

chemistry : the process whereby particles of liquids, gases, or solids intermingle as the result of their spontaneous movement caused by thermal (see thermal entry 1 sense 1b) agitation and in dissolved substances move from a region of higher to one of lower concentration

the diffusion of oxygen/carbon dioxide into soil

b physics

(1)

: reflection of light by a rough reflecting surface

(2)

: transmission of light through a translucent material : scattering

If you like astronomy, North Dakota can be a great place to view the night sky. After all, we have a lot of clear and cold nights, which translates to the colder it gets, the less diffusion of light.

—Northern Sentry

(3)

: the spread of energy throughout a material

the diffusion of heat in water

4

: the spread of cultural elements from one area or group of people to others by contact

Construction of these subterranean aqueducts spread in a … pattern of diffusion from Persia, to Oman, to … Yemen.

—Dale R. Lightfoot

The neighborhood is known for its diversity and cultural diffusion, historically populated by a number of immigrant groups.

—Claire Malon

5

photography : the process of slightly scattering light to give a pleasing artistic softness to a photograph

… perhaps the most fundamental parameter every photographer has to gain a mastery of is controlling the softness or hardness of the light. There are several ways to go about this, with one of them being diffusion.

—Alex Cooke

diffusional

di-ˈfyü-zhə-nᵊl 

adjective

Synonyms of diffusion

• diffuseness
• repetition
• repetitiveness
• periphrasis
• prolixity
• windiness
• garrulity

Examples of diffusion in a Sentence

the author's tendency toward diffusion makes the novel a tedious read

Recent Examples on the Web

But the practical race in 2026 is won by mastering both contests at once with absolute capability and radical efficiency, closed excellence and open diffusion, the biggest reliable compute and the smartest use of it. — Mark Minevich, Fortune, 21 Aug. 2026

The idea that knowledge generated inside a large subsidized investment does not stay contained to that one company suggests a form of knowledge diffusion outward to the businesses around it. — Nathan Goldman, Forbes.com, 20 Aug. 2026

Researchers assumed that corals were passive with respect to the slow-moving boundary layer, simply relying on natural diffusion through it to provide nutrients and oxygen. — Marlowe Starling, Quanta Magazine, 5 Aug. 2026

Even though these are technically a semi-sheer, the curtain panels can give you a bit more privacy and more of a light-filtering sheer than a true light diffusion. — Kate McGregor, Architectural Digest, 4 Aug. 2026

Word History

Etymology

Middle English diffusioun "outpouring (of speech)," borrowed from Late Latin diffūsiōn-, diffūsiō "pouring out (of liquids), watering of the eyes, abundance" (Latin, "geniality"), from Latin diffud-, variant stem of diffundere "to pour out over a wide surface, spread out, extend" + -tiōn-, -tiō, suffix of verbal action — more at diffuse entry 2

First Known Use

15th century, in the meaning defined at sense 2

Rhymes for diffusion

• allusion
• collusion
• conclusion
• confusion
• contusion
• delusion
• effusion
• exclusion
• extrusion
• illusion
• inclusion
• infusion

Kids Definition

diffusion

noun

dif·​fu·​sion dif-ˈyü-zhən 

1

: a diffusing or a being diffused

2

: the mixing of particles of liquids, gases, or solids so that they move from a region of high concentration to one of lower concentration

3

: the scattering of light by reflection from a rough surface or by passage through a translucent material (as frosted glass)

Medical Definition

diffusion

noun

dif·​fu·​sion dif-ˈyü-zhən 

1

: the process whereby particles of liquids, gases, or solids intermingle as the result of their spontaneous movement caused by thermal agitation and in dissolved substances move from a region of higher to one of lower concentration

2

a

: reflection of light by a rough reflecting surface

b

: transmission of light through a translucent material

diffusional

-ˈyüzh-nəl, -ən-ᵊl 

adjective