| birefringence | (noun) splitting a ray into two parallel rays polarized perpendicularly | Synonyms: double refraction |
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| carefreeness | (noun) the trait of being without worry or responsibility | - |
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| (noun) the cheerful feeling you have when nothing is troubling you | Synonyms: insouciance, lightheartedness, lightsomeness |
| forefront | (noun) the position of greatest importance or advancement; the leading position in any movement or field | Synonyms: cutting edge, vanguard |
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| (noun) the part in the front or nearest the viewer | Synonyms: head |
| 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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| refrain | (noun) the part of a song where a soloist is joined by a group of singers | Synonyms: chorus |
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| refresher | (noun) a course that reviews and updates a topic for those who have not kept abreast of developments | Synonyms: refresher course |
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| (noun) a drink that refreshes | - |
| (noun) a fee (in addition to that marked on the brief) paid to counsel in a case that lasts more than one day | - |
| refreshment | (noun) activity that refreshes and recreates; activity that renews your health and spirits by enjoyment and relaxation | Synonyms: recreation |
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| (noun) snacks and drinks served as a light meal | - |
| refrigerant | (noun) any substance used to provide cooling (as in a refrigerator) | - |
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| refrigeration | (noun) deliberately lowering the body's temperature for therapeutic purposes | - |
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| (noun) the process of cooling or freezing (e.g., food) for preservative purposes | Synonyms: infrigidation |
| refrigerator | (noun) white goods in which food can be stored at low temperatures | Synonyms: icebox |
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| storefront | (noun) the front side of a store facing the street; usually contains display windows | Synonyms: shopfront |
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