(pharmacy, medicine) A reaction to a medication that is unusual and unpredictable, specific to a particular person. Unlike allergy, it can occur on first exposure to the medication; unlike a side effect, it affects only very few individuals.

(chemistry) Any chemical reaction in which the concentration of some component varies over time or space in a regular periodic manner.

plural of reaction

(chemistry) any of many classes of reaction in which an atom or bond moves or migrates from a site in a reactant molecule to a different site in a product molecule

a power-generation prime mover having nozzles mounted on the moving element; turned by the reaction of the issuing fluid jet

(physics) Any nuclear reaction involving a photon and another subatomic particle

(chemistry) Any chemical reaction initiated by the absorption of a quantum of electromagnetic radiation to form an excited state

plural of reactant

All the changes in a tissue that result from the action of a foreign substance introduced into an organism

plural of redox reaction