solid

solid one of the three commonly recognized states in which matter occurs, i.e., that state, as distinguished from liquid and gas, in which a substance has both a definite shape and a definite volume. Solids resemble liquids in having a definite volume, but differ from both liquids and gases in having a definite shape. The molecules of a solid, like those of a liquid, are very close together, but whereas the molecules of a liquid are free to move around, those of a solid have less thermal energy and are held fixed in their places by intermolecular forces . Their only movement is a vibration about a fixed position. A solid changes to a liquid when its temperature is raised to its melting point . A definite quantity of heat (called the heat of fusion) is needed to change each gram of the substance from solid to liquid. Some substances change directly from solid to gas without passing through the liquid state (see sublimation ), but most change from solid to liquid before becoming gaseous. Solids are of various types. Metals, their alloys, some nonmetals, and ionic chemical compounds are crystalline in form. Some solids, e.g., chalk and clay, have no regular structure and are called amorphous. Substances such as pitch and resin are called semisolids; these are actually very viscid liquids, but their flow or change of shape is so slow at ordinary temperatures as to be scarcely discernible by the human eye (see viscosity ). Properties in which solids differ from one another include density, hardness, malleability, ductility, elasticity, brittleness, and tensile strength.

sol·id / ˈsälid/ • adj. (-id·er, -id·est) 1. firm and stable in shape; not liquid or fluid: the stream was frozen solid solid fuels. ∎  strongly built or made of strong materials; not flimsy or slender: a solid door with good, secure locks. ∎  having three dimensions: a solid figure with six plane faces. ∎  concerned with objects having three dimensions: solid geometry. 2. not hollow or containing spaces or gaps: a sculpture made out of solid rock a solid mass of flowers the stores were packed solid. ∎  consisting of the same substance throughout: solid silver cutlery. ∎  (of typesetting) without extra space between the lines of characters. ∎  (of a line or surface) without spaces; unbroken: the solid outline encloses the area within which we measured. ∎  (of time) uninterrupted; continuous: a solid day of meetings | it poured for two hours solid. 3. dependable; reliable: the defense is solid there is solid evidence of lower inflation. ∎  sound but without any special qualities or flair: the rest of the acting is solid. ∎  unanimous or undivided: they received solid support from their teammates. ∎  financially sound: the company is very solid and will come through the current recession. ∎  (solid with) inf. on good terms with: he thought he could put himself in solid with you by criticizing her. • n. a substance or object that is solid rather than liquid or fluid. ∎  (solids) food that is not liquid: she drinks only milk and rarely eats solids. ∎  Geom. a body or geometric figure having three dimensions. DERIVATIVES: sol·id·ly adv. sol·id·ness n.