What does dilatant mean?
Dilatant is a technical adjective describing substances that become thicker and more resistant to flow when subjected to force or rapid movement. A classic demonstration is a mixture of cornstarch and water: stirred gently it pours like a liquid, yet struck sharply it stiffens almost into a solid. This counterintuitive property, known in rheology as shear thickening, makes dilatant materials valuable in engineering applications such as protective body armour, which remains flexible during normal movement but hardens upon sudden impact. The word also carries an older, more general sense meaning simply 'tending to dilate' or expand, though this usage is rare outside specialized fields. Because dilatant appears mainly in scientific writing rather than casual conversation, it lends precision to discussions of fluid dynamics, soil behaviour, and material design. Understanding it offers a window into why some everyday substances — quicksand being a famous example — seem to defy our expectations of how liquids should behave.
(Of a substance) increasing in viscosity or resistance to flow when shear stress is applied; shear-thickening.
"The researchers tested whether the suspension was dilatant by measuring its response to rapid stirring."
Most common sense; used almost exclusively in scientific and engineering contexts.
Tending to dilate, expand, or widen.
"The physician noted the dilatant effect of the medication on the blood vessels."
Older and less common sense, largely confined to medical or physiological writing.
Stir it slowly and a dilatant fluid flows like liquid — punch it, and it turns solid enough to run across. That's the science behind 'walking on water' videos made of cornstarch.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of dilatant
Dilatant derives from the Latin verb 'dilatare', meaning 'to spread out' or 'enlarge', formed from 'dis-' ('apart') and 'latus' ('wide'), the same root that gives English 'latitude'. The adjective entered English in the seventeenth century through the participial stem 'dilatant-' of Latin 'dilatare', alongside its noun form 'dilatancy', which nineteenth-century physicists adopted to describe volume changes in granular media. It is thus cognate with 'dilate', 'dilatation', and 'dilation', all sharing the notion of widening or expansion.
Related word forms
How dilatant is actually used
Primarily used in technical and scientific contexts — rheology, physics, materials science, and soil mechanics — rather than everyday speech. In rheology, 'dilatant' is essentially synonymous with 'shear-thickening'.
Easily confused with dilatant
Dilatory describes slow, procrastinating behaviour, while dilatant refers to expansion or to fluids that thicken under stress.