|the first menstrual period; the establishment of menstruation|
|a period of sleep during which most dreaming occurs as the eyes move under closed lids and the skeletal muscles are deeply relaxed|
|1.||a response to some foregoing action or stimulus|
|2.||the reciprocal action of two things acting together|
|3.||opposition to change, esp political change, or a desire to return to a former condition or system|
|4.||a response indicating a person's feelings or emotional attitude|
|a. Compare side effect any effect produced by the action of a drug, esp an adverse effect|
|b. any effect produced by a substance (allergen) to which a person is allergicthe simultaneous equal and opposite force that acts on a body whenever it exerts a force on another body|
|6.||chemical reaction short for nuclear reaction|
|7.||stock exchange a sharp fall in price interrupting a general rise|
|usage Reaction is used to refer both to an instant response (her reaction was one of amazement) and to a considered response in the form of a statement (the Minister gave his reaction to the court's decision). Some people think this second use is incorrect|
reaction re·ac·tion (rē-āk'shən)
A response of an organism or living tissue to a stimulus.
The state resulting from such a response.
A chemical change or transformation in which a substance decomposes, combines with other substances, or interchanges constituents with other substances.
The response of cells or tissues to an antigen, as in a test for immunization.
A pattern of behavior constituting a mental disorder or personality type.
|reaction (rē-āk'shən) Pronunciation Key