diffuser

American  

[dih-fyoo-zer] / dɪˈfyu zər /

Or diffusor

noun

1. a person or thing that diffuses.

2. (in various machines or mechanical systems, as centrifugal pumps or compressors) a device for utilizing part of the kinetic energy of a fluid passing through a machine by gradually increasing the cross-sectional area of the channel or chamber through which it flows so as to decrease its speed and increase its pressure.

3. (in a lighting fixture) any of a variety of translucent materials for filtering glare from the light source.

4. a pierced plate or similar device for distributing compressed air for aeration of sewage.

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diffuser British  

/ dɪˈfjuːzə /

noun

1. a person or thing that diffuses

2. a part of a lighting fixture consisting of a translucent or frosted covering or of a rough reflector: used to scatter the light and prevent glare

3. a cone, wedge, or baffle placed in front of the diaphragm of a loudspeaker to diffuse the sound waves

4. a duct, esp in a wind tunnel or jet engine, that widens gradually in the direction of flow to reduce the speed and increase the pressure of the air or fluid

5. photog a light-scattering medium, such as a screen of fine fabric, placed in the path of a source of light to reduce the sharpness of shadows and thus soften the lighting

6. a perforated plate or similar device for distributing compressed air in the aeration of sewage

7. a device, attached to a hairdryer, which diffuses the warm air as it comes out

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Etymology

Origin of diffuser

First recorded in 1670–80; diffuse + -er ¹

Example Sentences

Consider the overbalance of gloss-black surfaces—not just the grille form but the roof, roof racks, roof pillars, bumpers, mirror caps, rear diffuser thingy, deep-tinted rear glass and heavy window masking.

From The Wall Street Journal • May 30, 2026

The fundamental aerodynamic philosophy is a return to so-called 'step-plane' cars, with a flat bottom either side of the central chassis reference plane, with a diffuser at the back.

From BBC • Dec. 9, 2025

Putting essential oils in a diffuser is also an option to revitalize your space.

From Salon • Jan. 1, 2024

Spices, musk and golden amber evoke a nice vibe in Pura’s Winter Noir diffuser refill.

From Washington Times • Dec. 6, 2023

The styling and drying process was extremely complicated—Mari wrapped individual strands of hair around the handle of a comb and then used a hairdryer with a diffuser attachment on each individual curl.

From "Keeping Pace" by Laurie Morrison