Liquus

Liquus is a Latin adjective meaning "liquid, fluid, clear" and was used in classical Latin to describe substances that flow or are not solid. The masculine form is liquus, the feminine liqua, and the neuter liquidum. In Latin texts the word could describe both liquids and figures described as liquid in character, and it appears in medical and alchemical writings as well as in descriptions of fluids.

In modern science and terminology, the root survives in several technical terms. The compound form liquus is not used by itself in technical literature, but related forms such as liquidus appear in metallurgy and materials science to denote the temperature or boundary above which a substance is completely liquid; on a phase diagram, the liquidus line separates liquid from mixed or solid phases. The term also underlies the English word liquid and related forms such as liquidity, as well as many Romance-language equivalents like Spanish líquido, French liquide, and Italian liquido.

In taxonomy or nomenclature, Latin adjectives historically appear as descriptive epithets, sometimes derived from liquus, but the term is not a common independent label in contemporary biology or chemistry outside of the specific "liquidus" usage.