Flüssig

Flüssig is a German adjective describing the liquid state of matter. It denotes substances that can flow, have a definite volume but no fixed shape, and adapt to the shape of their container. Liquids are distinct from solids, which have a definite shape, and from gases, which fill the available volume and typically expand to fill their container. The property of fluids to flow arises from the movement of their particles past one another and is quantified by viscosity. Liquids are relatively incompressible, though compressibility exists and varies with pressure and temperature. Temperature changes can cause phase transitions: heating may cause evaporation into gas, while cooling can lead to solidification.

In everyday language, flüssig can refer to anything in a liquid state, such as water, oil, or mercury. It also occurs in metaphorical uses, for example describing fluent speech or writing as flüssig or a flüssig geschriebener Text. In finance, Flüssigkeit or flüssig as a modifier relates to liquidity—assets that can be readily converted to cash, with the noun Liquidität.

Etymology: The word derives from a sense of flowing, related to fließen and to Fluss (river). In scientific use, Flüssigkeit is the noun for a liquid substance, while flüssig is the state adjective.