, pl. formulas, formulae (1) A recipe or prescription containing directions for the compounding of a medicinal preparation. (2) In chemistry, a symbol or collection of symbols expressing the number of atoms of the element or elements forming one molecule of a substance; sometimes also included is information on characteristics such as the arrangement of the atoms within the molecule, the atoms' electronic structure and their charge, and the nature of the bonds within the molecule. (3) An expression by symbols and numbers of the normal order or arrangement of parts or structures. (4) A mathematic relationship or principle, typically provided through use of an equation. [L. dim. of forma, form]