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

plural

F's, Fs, f's, fs

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

The cybersecurity company’s earnings and revenue forecast met analysts’ expectations but f ailed to impress investors.

From Barron's • Nov. 20, 2025

Thompson has instituted a curfew around the facility, allowing protests to occur only between f 9 a.m. and 6 p.m.

From Los Angeles Times • Oct. 10, 2025

In Welsh a single f is pronounced as a v — it takes two fs to make the noise in “fight” — and the emphasis is always on the penultimate syllable.

From Salon • May 27, 2024

An early stage that involved cyanobacteria innovating a new pigment, chlorophyll f, enabling the photosystem to harvest far-red light for the first time.

From Science Daily • Nov. 28, 2023

Black lampposts line the pier, each one curved to look like the letter f.

From "Kwame Crashes the Underworld" by Craig Kofi Farmer