1
: capable of flowing freely like water
fluid lava
a substance in a fluid state
2
—used to describe something that can change easily or that changes often
Boundaries between the farms were very fluid.
a fluid situation
3
: having or showing a smooth and easy style : graceful
a dancer's fluid movements
the sculpture's fluid lines
plural fluids
: a substance that is able to flow freely : a liquid substance
Please check the fluids in the car's engine.
She needs to drink plenty of fluids.
Fluid leaked from the car's engine.
a bottle of yellow fluid
Cite this Entry
“Fluid.” Merriam-Webster.com Simple Definition, Merriam-Webster, https://www.merriam-webster.com/simple/fluid. Accessed 16 Apr. 2026.
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