| diffraction | (noun) when light passes sharp edges or goes through narrow slits the rays are deflected and produce fringes of light and dark bands | - |
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| fracas | (noun) noisy quarrel | Synonyms: affray, altercation |
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| fracking | (noun) a well-stimulation technique in which rock is fractured by a pressurized liquid | - |
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| fractal | (noun) (mathematics) a geometric pattern that is repeated at every scale and so cannot be represented by classical geometry | - |
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| fraction | (noun) a small part or item forming a piece of a whole | - |
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| (noun) the quotient of two rational numbers | - |
| (noun) a component of a mixture that has been separated by a fractional process | - |
| fractionation | (noun) separation into portions | - |
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| (noun) a process that uses heat to separate a substance into its components | Synonyms: fractional process |
| fractiousness | (noun) the trait of being prone to disobedience and lack of discipline | Synonyms: unruliness, wilfulness, willfulness |
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| fracture | (noun) the act of cracking something | Synonyms: crack, cracking |
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| (noun) (geology) a crack in the earth's crust resulting from the displacement of one side with respect to the other | Synonyms: break, fault, faulting, geological fault, shift |
| (noun) breaking of hard tissue such as bone | Synonyms: break |
| infraction | (noun) a crime less serious than a felony | Synonyms: infringement, misdemeanor, misdemeanour, violation |
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| refraction | (noun) the amount by which a propagating wave is bent | Synonyms: deflection, deflexion |
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| (noun) the change in direction of a propagating wave (light or sound) when passing from one medium to another | - |
| refractiveness | (noun) the physical property of a medium as determined by its index of refraction | Synonyms: refractivity |
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| refractivity | (noun) the physical property of a medium as determined by its index of refraction | Synonyms: refractiveness |
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| refractometer | (noun) measuring instrument for measuring the refractive index of a substance | - |
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| refractoriness | (noun) the trait of being unmanageable | Synonyms: recalcitrance, recalcitrancy, unmanageableness |
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| refractory | (noun) lining consisting of material with a high melting point; used to line the inside walls of a furnace | Synonyms: furnace lining |
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