English Reference

Word

mucus

Phoneticsmu·cus

US/ˈmjukəs/

UK/mjˈuːkəs/

Definitions

01bodily secretion

B2 · Medicine

n. the slippery liquid made by your body to protect your nose, throat, and stomach.

n. a viscid secretion produced by the mucous membranes, consisting of water, mucins, and inorganic salts, which serves to lubricate and protect tissues.

“When you have a cold, your body produces more mucus to help fight the infection.”

“The respiratory system relies on a thin layer of mucus to trap inhaled particles and pathogens before they can reach the lungs.”

Technical

Usage

Uncountable in general usage; plural 'mucuses' is rare and restricted to medical contexts describing different types.

Pitfall

The mucus membrane was irritated.

The mucous membrane was irritated.

Use 'mucus' as the noun (the substance) and 'mucous' as the adjective (the type of tissue).

Teaching tip

Learners often confuse the spelling of the noun 'mucus' with the adjective 'mucous'. Point out that the -ous ending is a common adjective marker in English.

Synonyms

phlegmslime

02plant substance

C1 · Science

n. a sticky substance found in some plants that helps them hold water.

n. a gelatinous substance found in certain plants, often referred to as mucilage, which aids in water retention.

“The thick mucus inside the aloe vera leaf is used to soothe burnt skin.”

“Botanists observed that the desert plant secreted a thick mucus to prevent dehydration during the peak of the dry season.”

Technical

Usage

Often used interchangeably with 'mucilage' in botanical descriptions.

Teaching tip

This sense is quite specialized; for general purposes, 'sap' or 'gel' is more common when talking about plants.

Synonyms

mucilagegum

Real-World Examples

“The yellow slime, sticky but more watery than human mucus, is a soup of sugars and proteins.”
The Guardian · 8 Sept 2026
“Gut microbes need something to eat, and when fiber is limited, they may begin consuming proteins from the mucus lining that protects the gut.”
ScienceDaily · 15 Aug 2026

Etymology

Learned borrowing from Latin mūcus. Partly displaced Old English slīm, whence modern slime.

Etymology adapted from Wiktionary, available under CC BY-SA 4.0.

Word family

mucousAdjectivemucusNoun

Related words

Domain

Botany

This entry

Level
C1 · Advanced
Frequency
Occasional
Updated

Scan code

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English Reference