What does colloid mean?
A colloid is a type of mixture in which extremely fine particles — typically between one nanometre and one micrometre across — are spread evenly throughout another substance without dissolving or settling out. Everyday examples include milk (fat droplets in water), fog (water droplets in air), gelatin, and mayonnaise. Although colloids look uniform to the naked eye, they differ from true solutions because their particles are large enough to scatter light, an effect known as the Tyndall phenomenon. The term comes from the Greek kolla, meaning glue, reflecting how early nineteenth-century chemists first studied gelatinous materials that resisted crystallisation. Colloids matter far beyond the laboratory: they underpin food science, paint formulation, soil behaviour, water treatment, and many biological processes. In medicine, the word can also refer to the protein-rich material stored within the thyroid gland.
A mixture in which microscopically dispersed insoluble particles are suspended throughout another substance, neither dissolving nor settling.
"Gelatin desserts owe their texture to a colloid of protein molecules trapped in water."
In medical contexts, 'colloid' additionally denotes the gelatinous material stored in thyroid follicles.
Relating to or having the character of a colloid; colloidal.
"The colloid state lies between true solutions and coarse suspensions."
The form 'colloidal' is now strongly preferred for adjectival use.
Regular plural; commonly used when discussing classes or types of colloidal systems.
"Chemists classify colloids into sols, gels, emulsions, foams, and aerosols."
The word 'colloid' literally means 'glue-like' — coined from Greek kolla ('glue') because early chemists noticed gelatinous substances like glue refused to behave like ordinary solutions.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of colloid
The word 'colloid' was coined in the mid-nineteenth century by the Scottish chemist Thomas Graham, who derived it from the Greek kolla ('glue') plus the suffix -oid ('resembling'), because substances like gelatin and gum behaved unlike ordinary crystalline solutes. It entered English scientific vocabulary around the 1860s as chemists began systematically studying these dispersed systems. The Greek root kolla also gives us 'collagen' and, via French, 'collage'.
Related word forms
How colloid is actually used
Primarily a technical term used in chemistry, physics, biology, and medicine; rare in casual conversation. The adjective 'colloidal' is more common than the noun in everyday scientific writing.
Easily confused with colloid
Collodion is a specific syrupy solution of nitrocellulose used in photography and medicine, whereas a colloid is any two-phase dispersed system.