What does daltonism mean?
Daltonism is a noun referring to colour blindness, particularly the inherited inability to distinguish between red and green. Named after the English chemist John Dalton, who published the first scientific account of the condition after realising he suffered from it himself, the word carries both technical and historical resonance. It is used in medical contexts to describe congenital colour-vision deficiency, though everyday speakers usually prefer the plainer term 'colour blindness'. Someone with daltonism may struggle with tasks that depend on reliable colour perception, such as interpreting traffic signals, reading coloured charts, or choosing coordinated clothing. The condition is far more common in men than women because it is linked to the X chromosome. Related forms include 'daltonian', and the same scientist's name survives independently in physics as the unit of atomic mass, the dalton.
nounA form of colour blindness, especially red-green colour blindness, in which a person cannot distinguish certain colours, particularly reds and greens. The term is used both medically and more loosely for any inherited deficiency in colour vision.
- Colour blindness, especially red-green colour blindness, in which reds and greens cannot be reliably distinguished.
- More broadly, any congenital deficiency of colour vision.
"His undiagnosed daltonism went unnoticed until he confused a red traffic light with an amber one during his driving test."
"Because of his daltonism, he had always relied on his sister to pick out matching clothes."
"The airline's medical screening detected a mild daltonism that ruled out a career as a commercial pilot."
Rarely pluralised; the uncountable singular form is standard even when referring to multiple cases or types of the condition.
"Clinicians distinguish several distinct daltonisms according to which cone cells are affected."
The word honours John Dalton — who was himself colour-blind, and whose 1794 study of his own defective vision was the first scientific paper ever written on the condition.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of daltonism
The word derives from the name of the English chemist and physicist John Dalton (1766–1844), who was himself red-green colour-blind and published the first detailed scientific description of the condition in 1794, based on his own and his brother's experience. The suffix '-ism' was added to form a term for the condition, by analogy with other medical terms. The same eponym gives us 'daltonian' as an adjective and, separately, the physics unit 'dalton'.
Word family
Usage notes
Daltonism is somewhat formal or technical in register; in everyday speech most people simply say 'colour blindness' (or 'color blindness'). It is chiefly British in frequency but understood internationally. In strict medical usage it refers specifically to red-green deficiencies rather than total colour blindness.
Don't confuse with
Deuteranopia is one specific subtype of red-green colour blindness caused by abnormal green cone cells, whereas daltonism is the broader umbrella term for such colour-vision deficiencies.