ACT Vocabulary List part 7

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Radian: a unit of angle measure within a circle

Radiate: to emit energy or light that extends from a single source

Radii: the plural form of radius

Radioactive decay: a natural process by which an atom of a radioactive isotope spontaneously decays into another element

Radius: a line segment with endpoints at the center of the circle and on the perimeter of the circle, equal to one-half the length of the diameter

Rapid: moving very quickly

Rapt: being completely occupied by, or focused on, something

Ratio: a comparison between two quantities (for example, the ratio of girls to boys in the class is 1:2)

Real number line: an infinite line of real numbers represented on a one-dimensional graph

Real numbers: numbers that can be associated with points on a number line

Recount: to describe the facts or details of a past event; to retell a story or repeat testimony

Rectangular: having the shape of a rectangle (a parallelogram with four right angles)

Recurrent: taking place over and over

Redeem: to pay off a debt or fulfill an obligation; to make good

Redirect: to alter the course or direction

Rediscover: to learn about or see something as though for the first time

Regular hexagon: a six-sided figure with congruent sides and angles

Relevant: logically connected; pertinent

Reluctant: unwilling and resistant

Reparation: compensation given to make amends

Resonate: to produce or amplify vibrations

Respectively: in the order given

Retention: the ability to hold things in or retain

Rifling: (v.) to search through, looking for something to steal; (n.) the spiral grooves on the inside of a gun barrel

Rift: a split or a break

Rotate vs. Revolve: rotate: to turn about a fixed point; revolve: to turn on an axis

Rudimentary: very basic or not fully developed


Sacrilege: to misuse something that is sacred

Sanctuary: a sacred place; a refuge

Saplings: young trees

Saturation: a state of being completely full or soaked

Sauropod: a type of plant-eating dinosaur, for example, the brontosaur

Scientific inquiry: based on experiment and observation and the application of the Scientific Method; examination into facts or principles

Scrutiny: very close examination

Sediment: solid materials that sink to the bottom of a liquid

Seedling: a young plant grown from seed

Seminal: forms the basis for future development; at the beginning; original

Simultaneously: happening or existing at the same time

Skepticism: an attitude of doubt or disbelief

Social rituals: specific gestures and behaviors that are observed by members of a community

Solace: comfort; safety

Solid: neither gas nor liquid; of definite shape and volume

Solute: a dissolved substance

Solution: a mixture of two or more substances

Solution set: the set of values that make an equation true

Sovereign: (adj.) having supreme power; (n.) ruler or king

Span: distance between two things

Specific gravity: the ratio of the density of one substance to the density of another substance

Speculators: people who form theories based on uncertain evidence; those who purchase something with the hope of reselling it later at a profit

Sphere: a solid, round figure where all points on the surface are the same distance from the center (for example, a basketball)

Spleen: a vascular, ductless organ that is located in the left abdominal region close to the stomach

Stagnant: not moving or changing; stale

Standard (x, y) coordinate plane: a plane that is formed by a horizontal x-axis and a vertical y-axis that meet at point (0,0) (also known as the Cartesian Coordinate Plane)

Steerage passenger: someone who rides in the least expensive section of a ship

Straddle: having one leg on each side of something

Stratosphere: a layer of the atmosphere between the troposphere and mesosphere

Subcontractor: someone who agrees to perform one part of a larger commitment or contract

Subjective: dependant on a person's attitudes or opinions

Subsequent: to come next or later

Subtropical: near the tropical areas of the world; extremely humid and hot climate

Sucrose: a simple sugar

Summary: (n.) a statement that has condensed a larger body of work; (adj.) conducted without trial

Supercooled: below freezing but remaining liquid

Suspensions: the state of a substance when its particles are combined together but have not been dissolved in a fluid or solid

Sustenance: things that provide nourishment for survival

Synchronized: occurring at the same time and at the same rate

Synthesis: combining separate elements to form a whole

Synthetic polymer: a human-made, repeating chain of atoms

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