noun

a substance that has no fixed shape and yields easily to external pressure; a gas or (especially) a liquid.

body fluids

flowing substance,liquid,watery substance,moisture,solution,juice,sap,gas,gaseous substance,vapour

adjective

(of a substance) able to flow easily.

the paint is more fluid than tube watercolours

flowing,able to flow easily,liquid,liquefied,melted,molten,uncongealed,running,gaseous,gassy,fluxional