fluidity

Etymology

The OED and the Shorter Oxford take it as formed from English fluid + -ity, comparing French fluidité;^[2][3][4] Merriam-Webster considers it probably a borrowing of the French word, from Middle French,^[5] and Etymonline allows either route.^[6] Johnson already gave it as French fluidité, from fluid.^[7] Fluid is from Old French fluide and directly from Latin fluidus (“flowing, moist”), from fluō (“to flow”).^[6]

Earliest recorded meaning

Of speech or writing, the quality of flowing easily and clearly: 1603, in John Florio's translation of Montaigne's Essayes.^[2] Merriam-Webster also dates the word to 1603,^[5] and Etymonline puts both the physical and the figurative uses about 1600, the figurative one following French.^[6]

Semantic evolution

The physical sense, the quality or condition of being fluid, is recorded from 1605, in Thomas Tymme's translation of Joseph Du Chesne's Practise of Chymicall Physicke.^[2] Johnson (1755) defined it as the quality opposite to solidity and quoted Newton's Opticks on how heat makes bodies more fluid.^[7] From 1824 it was used figuratively of things that are not physical,^[2] for changeableness, instability or flexibility,^[3][5] and in physics it became the name of the reciprocal of viscosity.^[5][8]

Timeline

• 1603 – of speech or writing, the quality of flowing easily.^[2][5]
• 1605 – the quality or condition of being fluid.^[2]
• 1824 – figuratively, of things that are not physical: changeability.^[2][3]

Meanings

Noun

1. The quality or state of being fluid, able to flow like a liquid or gas.^[5][8][2]
2. In physics, a measure of how readily a substance flows, the reciprocal of viscosity.^[5][8]
3. Changeable or unsettled quality; flexibility or easy adaptability: the fluidity of the political situation.^[5][3]
4. Smooth and graceful flowing quality, as of movement, style or speech: the fluidity of her brushwork.^[5][3][2]

Related words

• fluent
• fluency

References

1. ^ a b Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e f g h i Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
3. ^ a b c d e Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
4. ^ Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
5. ^ a b c d e f g h i Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
6. ^ a b c Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
7. ^ a b Johnson, Samuel (1755), A Dictionary of the English Language, London; 4th ed. 1773; Johnson's Dictionary Online, ed. Beth Rapp Young et al.
8. ^ a b c Collins English Dictionary (2023), Glasgow: HarperCollins