(physics) An excited state of an isotope, often having different a spin quantum number (designated with an m)

An isotopic signature

plural of isotope dilution

(chemistry) Any of a set of structural isomers that are related by a pericyclic reaction

(physics) A system that does not interact with its surroundings. Depending on context this may mean that its total energy and/or momentum stay constant. In thermodynamics, isolated is usually used to indicate that the system's energy does not change. In mechanics it is used to indicate that the system's momentum does not change.

(physics, chemistry) A feature of the absorption spectra of a mixture of substances that are reacting with each other, in that at one frequency the absorption will remain constant throughout the reaction

plural of isosceles trapezoid

A quadrilateral with two parallel sides and a separate pair of congruent sides which are not parallel.

plural of isoabsorption

(linguistics) A natural language with no proven genetic relationship to another language.