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Browse key terms and definitions across all GCSE subjects. Search by keyword or filter by subject and exam board.
23,110 key terms
Adjacent
Sides or angles next to one another and sharing a vertex or side.
Adjacent angles
Angles next to one another that share a vertex and one side, without overlapping.
Adjacent side
The side next to the acute angle being considered in a right-angled triangle, excluding the hypotenuse.
Adjacent values
Values next to each other in a list.
Adjective
A word that describes or qualifies a noun, such as ‘gloomy’ in ‘a gloomy business’.
‘Adl
Divine justice: the belief that Allah always acts fairly and justly. Also called Adalat.
Administration
The organisation and management of a household, estate or government, including its people and resources.
Administrative data
Information collected through the operation of organisations or public services, such as visa, border, tax and benefits records, rather than through a survey designed specifically to measure migration.
Adolescence
The transition between childhood and adulthood, involving physical, cognitive, emotional and social changes.
Adoption
Bringing up a child who is not one’s biological child. In Silas Marner, Silas’s adoption of Eppie is presented through his everyday care rather than a modern legal process.
Adoption
A legal process through which someone becomes the parent of a child born to other parents.
Adoption
A political party’s formal acceptance of a selected person as its official candidate for an election.
Adoration
Prayer that praises God and acknowledges his greatness and goodness.
Adrenalin
A chemical messenger made by the adrenal glands that prepares the body for fight or flight.
Adrenalin
A hormone produced by the adrenal glands that prepares the body for fight or flight.
Adrenaline
A hormone released by the adrenal glands during fear or stress that prepares the body for rapid action.
Adrenaline
A hormone released by the adrenal glands during fear or stress that increases heart rate and the delivery of oxygen and glucose to the brain and muscles.
Adrenaline
A hormone involved in the body's response to stress or excitement. Beta blockers reduce its effects on the body.
Adsorption
The attachment of particles to the surface of a substance, such as silica gel in thin-layer chromatography.
Adult cell cloning
A cloning method in which the nucleus of an adult body cell is inserted into an egg cell whose own nucleus has been removed.
Adulteration
Adding other substances to food or drink, often to increase the amount sold or disguise poor quality.
Adultery
Sexual relations involving a married person and someone other than their spouse.
Adultery
Sexual unfaithfulness to a husband or wife.
Adultery
A sexual relationship between a married person and someone who is not their spouse.
Adult stem cell
A stem cell retained in a mature animal; adult stem cells in bone marrow can form many cell types, including blood cells.
Adult stem cell
A stem cell found in an adult animal that can replace cells and differentiate into a more limited range of cell types than an embryonic stem cell.
Advaita
A non-dual Hindu philosophical tradition which understands ultimate reality as Brahman and regards apparent separateness as not ultimately real.
Advaita Vedanta
A Hindu philosophical tradition which teaches that atman and Brahman are ultimately identical.
Advanced country (AC)
A country with a relatively highly developed economy, generally high average incomes and extensive services.
Advent
The period of preparation for Christmas, beginning on the fourth Sunday before Christmas.
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