ACT Vocabulary List part 4

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Fahrenheit: a temperature scale that measures the boiling point of water at 212 degrees and the freezing point at 32 degrees

Feign: to fabricate or deceive

Fermentation: the chemical process of breaking down an organic substance into simpler substances such as the fermentation of sugar to alcohol

Fickle: constantly changing one's mind

Fjord: an inlet lined by steep slopes that is long, narrow, and deep

Fledgling: a young bird that has just acquired feathers; also used to describe an inexperienced newcomer

Flourish: (v.) to prosper; (v.) to thrive; (n.) a dramatic gesture; (n.) a written embellishment

Foil: (n.) a character whose traits exemplify the opposite traits of another character when they are compared; (v.) to prevent an action, often by ruining a plan; (n.) a weapon used in the sport of fencing

Foliation: the alternating layers of different mineral compositions within solid rocks

Forecast: to predict future events, such as the weather

Foresee: to know beforehand

Foreshadow: to suggest or hint at future occurrences

Forgo: to refrain from doing something previously planned

Formalize: to make something official or valid

Franchise: a right given to an individual or group to operate a branch of a business and sell the business' products; the right to vote

Frenzied: in a temporary crazed state

Friction: the force resistant to motion

Frivolous: unnecessary and silly


Gable: the triangular section of a wall that fills the space between the two slopes of a roof

Galvanism: a direct electrical current produced by chemical reactions

Gas: a fluid (such as air) that is not independent in shape or volume but tends to expand

Gas chromatograph: a device used to detect the composition of an unknown material

Gastric emptying: the movement from the stomach to the small intestine, and finally into the colon

Gaudy: tastelessly flashy

Glacial: relating to a glacier; callous and cold; extremely slow

Glib: doing something with ease and slickness, but lacking sincerity

Gravity: the force of attraction between two bodies of mass

Gypsum: a yellowish-white mineral used to make plaster


Haggle: to bargain in an annoying manner; to harass

Halitosis: the condition of having breath with a foul odor

Harbinger: a sign that foreshadows upcoming events

Herbivorous: a plant-eating organism

Hindu: (adj.) relating to the religion of Hinduism, which originated in India; (n.) a person who practices Hinduism

Hoist: to lift up

Homeric epic: a classic Greek tale of heroism written by the ninth-century Greek author, Homer

Hue: color

Humidity: a measure of how damp the air is

Hydraulic: operated by using water or fluid pressure

Hydrogen bonding: the chemical bonding of a hydrogen atom with another electronegative atom

Hypotenuse: the longest side of a right-angle triangle, which is always the side opposite the right angle


Ideological: relating to the fundamental ideas of an individual or group

Idiosyncrasy: a peculiar characteristic

Igneous rock: rock that is formed by the cooling and solidification of molten magma

Ignition temperature: the temperature that a fuel must reach before combustion can begin

Immerse: to completely submerge

Imminent: close to happening; impending

Imply: to indirectly suggest, often confused with infer, which means "to conclude"

Improvise: to do or perform without preparation; to create something only from readily available materials

Inalienable: impossible to take away

Inauguration: a formal initiation or induction

Incarcerate: to imprison

Incinerate: to set fire to and burn something until it is reduced to ashes

Inclined: disposed to a certain path of thought; sloping

Inconstant: not following a pattern; varying

Incorporate: to bring two things or certain aspects of two things together

Indifference: total lack of concern or interest

Indigenous: native to or naturally existing in a certain area

Indignation: anger due to unfairness

Indulge: to freely partake in; to yield to the wish or desire of oneself or others

Inevitable: bound to happen; unavoidable

Inexhaustible: plentiful; impossible to use up completely

Inexplicable: impossible to give the reason for; unexplainable

Infer: to deduce from evidence, often confused with imply

Infirmary: a small hospital, often in an institution, used to provide care for the sick

Infrared: light energy having a wavelength below the visible range; it is experienced as heat

Infuse: for one substance to penetrate into another (for example, steak infused with garlic flavor)

Ingenious: brilliant and clever

Inherent: naturally occurring, permanent element or attribute

Inscribe: to write or engrave words on a surface; to write one's name on something

Insinuate: to subtly imply

Institute: (v.) to enact or establish; (n.) an organization

Institution: an establishment; a pillar of society (for example, the institution of marriage)

Interior angle: an angle inside of a shape (that is, all of the interior angles in a triangle add up to 180 degrees)

Intern: one who is confined during wartime against his or her will; a student or recent graduate working as an apprentice in a certain professional field

Interpret: to translate or explain a concept

Interpretation: a personal explanation for another's creation, such as a play or poem

Interstitial: (n.) fluid outside of cells; (adj.) occupying the small spaces between objects; (adj.) occurring during the short time periods between events

Intracellular: within a cell or cells

Intricacy: a detail of something complex

Invaluable: priceless

Involuntary: an action done without one's consent or free will

Irony: use of words to express a meaning that is the opposite of the real meaning; similar to and often confused with sarcasm, which means "words used to insult or scorn"

Irreconcilable: impossible to adjust or compromise

Irrelevant: not relevant or pertinent; outside the scope of a discussion or argument

Irrevocable: impossible to reverse

Isosceles triangle: a triangle with two congruent sides and two congruent angles

Isotopes: two or more atoms with an identical atomic number and differing in number of electrons

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