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• f
  f

  abbreviation

  firm.
• F
  F

  noun

  the sixth letter of the English alphabet, a consonant.
• f/
  f/

  abbreviation

  f-number.
• F-
  F-

  abbreviation

  (in designations of aircraft) fighter.
• f.
  f.

  abbreviation

  (in prescriptions) make.
• F.
  F.

  abbreviation

  Fahrenheit.

f

¹ American  

abbreviation

1. firm.

2. Photography. f-number.

3. Music. forte.

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f ² American  

Symbol.

1. Optics. focal length.

2. Mathematics. function (of). See function.

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F ³ American  

[ef] / ɛf /

Or f

noun

F's, plural Fs, plural f's, plural fs plural

1. the sixth letter of the English alphabet, a consonant.

2. any spoken sound represented by the letter F or f, as in fat, differ, or huff.

3. something having the shape of an F .

4. a written or printed representation of the letter F or f.

5. a device, as a printer's type, for reproducing the letter F or f.

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F ⁴ American  

abbreviation

1. female.

2. Genetics. filial.

3. firm.

4. franc; francs.

5. French.

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F ⁵ American  

Symbol.

1. the sixth in order or in a series.

2. (sometimes lowercase) (in some grading systems) a grade or mark that indicates academic work of the lowest quality; failure.

3. Music.

   1. the fourth tone in the scale of C major or the sixth tone in the relative minor scale, A minor.

   2. a string, key, or pipe tuned to this tone.

   3. a written or printed note representing this tone.

   4. (in the fixed system of solmization) the fourth tone of the scale of C major, called fa.

   5. the tonality having F as the tonic note.

4. (sometimes lowercase) the medieval Roman numeral for 40.

5. Fahrenheit.

6. Mathematics.

   1. field.

   2. function (of). See function.

7. (sometimes lowercase) farad.

8. Chemistry. fluorine.

9. (sometimes lowercase)

   1. force.

   2. frequency.

   3. fermi.

10. Biochemistry. phenylalanine.

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f/ ⁶ American  

Or f/ or f:

abbreviation

Photography.

1. f-number.

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F- ⁷ American  

abbreviation

Military.

1. (in designations of aircraft) fighter.

   F-105.

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f. ⁸ American  

abbreviation

1. (in prescriptions) make.

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f. ⁹ American  

abbreviation

1. (in prescriptions) let them be made.

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f. ¹⁰ American  

abbreviation

1. (in prescriptions) let it be made; let there be made.

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f. ¹¹ American  

abbreviation

1. (in the Netherlands) guilder; guilders.

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f. ¹² American  

abbreviation

1. farad.

2. farthing.

3. father.

4. fathom.

5. feet.

6. female.

7. feminine.

8. filly.

9. fine.

10. fluid (ounce).

11. folio.

12. following.

13. foot.

14. form.

15. formed of.

16. franc.

17. from.

18. Mathematics. function (of ).

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F. ¹³ American  

abbreviation

1. Fahrenheit.

2. February.

3. Fellow.

4. forint.

5. franc; francs.

6. France.

7. French.

8. Friday.

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F ¹ British  

symbol

1. music

   1. a note having a frequency of 349.23 hertz ( F above middle C ) or this value multiplied or divided by any power of 2; the fourth note of the scale of C major

   2. a key, string, or pipe producing this note

   3. the major or minor key having this note as its tonic

2. Fahrenheit

3. Fellow

4. chem fluorine

5. Helmholtz function

6. physics force

7. franc(s)

8. farad(s)

9. genetics a generation of filial offspring, F 1 being the first generation of offspring, F 2 being the second generation, etc

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abbreviation

1. France (international car registration)

f ² British  

symbol

1. music forte: an instruction to play loudly

2. physics frequency

3. (formerly in the Netherlands) guilder

4. maths function (of)

5. physics femto-

6. chess See algebraic notation

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f. ³ British  

abbreviation

1. fathom(s)

2. female

3. grammar feminine

4. folio

5. following (page)

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f ⁴ British  

/ ɛf /

noun

1. the sixth letter and fourth consonant of the modern English alphabet

2. a speech sound represented by this letter, usually a voiceless labio-dental fricative, as in fat

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F- ⁵ British  

abbreviation

1. fighter

   F-106

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f ⁶ British  

symbol

1. f-number

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Etymology

Origin of f.⁸

From the Latin word fac

Origin of f.⁹

From the Latin word f īant

Origin of f.¹⁰

From the Latin word fiat

Origin of f.¹¹

From the Dutch word florin

Example Sentences

Secretary Robert F. Kennedy Jr. recently announced initiatives intended to rein in antidepressants.

From Los Angeles Times • May 18, 2026

Secretary of Health and Human Services Robert F. Kennedy Jr. has, historically, been very public about his concerns about what is plaguing the nation’s well-being.

From Salon • May 15, 2026

Health and Human Services Secretary Robert F. Kennedy Jr. said last month that the government would loosen regulations for about a dozen peptides.

From Barron's • May 11, 2026

Powell’s calm but forceful defense of Fed independence likely staved off larger attacks on the institution and won him admiration and awards, like the John F. Kennedy Profile in Courage award.

From MarketWatch • May 10, 2026

If this was a test, he couldn’t afford to get an F. He stumbled a few times as they ran for the river.

From "The Son of Neptune" by Rick Riordan