Noun

• S: (n) fluid (a substance that is fluid at room temperature and pressure)
• S: (n) fluid (continuous amorphous matter that tends to flow and to conform to the outline of its container: a liquid or a gas)

Adjective

• S: (adj) fluid, unstable (subject to change; variable) "a fluid situation fraught with uncertainty"; "everything was unstable following the coup"
• S: (adj) fluid, runny (characteristic of a fluid; capable of flowing and easily changing shape)
• S: (adj) fluent, fluid, liquid, smooth (smooth and unconstrained in movement) "a long, smooth stride"; "the fluid motion of a cat"; "the liquid grace of a ballerina"
• S: (adj) fluid, liquid (in cash or easily convertible to cash) "liquid (or fluid) assets"
• S: (adj) fluid, mobile (affording change (especially in social status)) "Britain is not a truly fluid society"; "upwardly mobile"