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English Words Starting With F

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Noun Verb Adjective Adverb Plural noun Combining form Verb (transitive)Verb (intransitive)Verb (ambitransitive)

flunitrazepam
nounVery Low
/ˌfluːnɪˈtreɪzəpæm/A potent sedative-hypnotic benzodiazepine drug.
flunk
nounverbverb-intransitive+1B2
/flʌŋk/to fail a test or course, especially at school or university
flunkey
nounC2/Rare
/ˈflʌŋki/A liveried servant or footman, especially one who is overly attentive or servile.
flunkout
nounMedium
/ˈflʌŋk aʊt/To leave school or a course because of failing grades.
flunky
nounC1
/ˈflʌŋki/A person who performs menial or routine tasks, especially one employed to run errands and do subordinate work; a lackey.
fluoborate
nounVery low
/ˌfluːə(ʊ)ˈbɔːreɪt/A salt or ester of fluoboric acid (HBF₄), containing the tetrafluoroborate anion BF₄⁻.
fluoboric acid
nounVery Low / Technical
/ˌfluːə(ʊ)ˈbɒrɪk ˈasɪd/An inorganic compound with the chemical formula HBF₄, a strong acid derived from boron trifluoride and water, often used as a catalyst or etchant in industrial processes.
fluon
nounLow. Primarily used in technical, engineering, and manufacturing contexts.
/ˈfluːɒn/Fluon is a brand name for polytetrafluoroethylene (PTFE), a synthetic fluoropolymer known for its non-stick properties and high resistance to heat and chemicals.
fluophosphate
nounVery Rare / Highly Technical
/ˌfluːə(ʊ)ˈfɒsfeɪt/A compound containing fluorine and phosphate groups.
fluophosphoric acid
nounC2 / Extremely Low
/ˌfluːə(ʊ)ˌfɒsˈfɒrɪk ˈæsɪd/A highly corrosive, inorganic chemical compound (HPO₃F) used as a catalyst or reagent in chemical synthesis.
fluor-
combining-formnounC2 / Very Rare
/ˈflʊə.rəʊ-/ or /ˈflʊə.rɒ-/A combining form relating to the element fluorine, or to fluorescence.
fluorapatite
nounC2
/ˌflʊərəʊˈæpətaɪt/A hard, crystalline mineral that is a form of calcium phosphate containing fluorine, and is the main component of tooth enamel and bone.
fluorene
nounVery Low
/ˈflʊəriːn/A colorless crystalline aromatic hydrocarbon, C13H10, derived from coal tar, used in the manufacture of dyes, resins, and insecticides.
fluoresce
verbverb-intransitiveLow
/ˌflʊəˈrɛs/To emit light of a different colour after absorbing light or other electromagnetic radiation.
fluorescein
nounC1
/ˌflʊəˈrɛs.i.ɪn/A synthetic organic compound used as a fluorescent dye in aqueous solution.
fluorescence
nounC1/C2
/ˌflɔːˈres.əns/The property of certain substances to emit visible light after absorbing light of a different, usually higher, wavelength. The emitted light stops almost immediately when the source of excitation is removed.
fluorescence-activated cell sorter
nounLow
/flʊəˌrɛsəns ˈæktɪveɪtɪd sɛl ˈsɔːtə/A specialized laboratory machine that separates and sorts individual biological cells based on whether they are fluorescing (emitting light) after being treated with a fluorescent dye or tag.
fluorescent
adjectivenounB2
/ˌflʊəˈrɛs(ə)nt/Emitting visible light after absorbing radiation from another source; glowing brightly under ultraviolet or other specific wavelengths.
fluorescent lamp
nounB2
/flɔːˌres.ənt ˈlæmp/A type of electric light that produces visible light by causing a phosphor coating inside a glass tube to fluoresce when excited by ultraviolet light generated by an electric discharge in mercury vapour.
fluorescent screen
nounC1+
/flʊəˌrɛsənt skriːn/A surface coated with fluorescent material that emits visible light when struck by radiation (such as X-rays or electron beams).

Showing 3261–3280 of 5868 words.