A continuous, amorphous substance whose molecules move freely past one another and that has the tendency to assume the shape of its container; a liquid or gas.
1. Of, relating to, or characteristic of a fluid.
2. Readily reshaped; pliable.
3. Smooth and flowing; graceful: the fluid motion of a cat.
a. Changing or tending to change; variable: a fluid situation fraught with uncertainty.
b. Characterized by or allowing social mobility: a fluid society.
5. Convertible into cash: fluid assets.
[From Middle English, flowing, from Old French fluide, from Latin fluidus, from fluere, to flow; see bhleu- in the Appendix of Indo-European roots.]
flu·idi·ty (-ĭdĭ-tē), fluid·ness n.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2019 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.