(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) a reaction in which radicals are added to both sides of a double or triple bond

(organic chemistry) The trans oxidation of an alkene, to form a dihydric alcohol, catalyzed by iodine and silver benzoate.

The state of diverse reception, when there are many who praise something while there are also many who dislike it. / (ironical) An unmixed reaction, usually opposition.

(chemistry) any reaction in which two (or more) molecules react with the resulting loss of a molecule of water (or other small molecule); the formal reverse of hydrolysis

(chemistry) the reaction of a halogen with a methyl-ketone to form a haloform

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

(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

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

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