f

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The sixth letter of the modern English alphabet.
• noun Any of the speech sounds represented by the letter f.
• noun The sixth in a series.
• noun Something shaped like the letter F.
• noun A grade that indicates failing status.
• noun The fourth tone in the scale of C major or the sixth tone in the relative minor scale.
• noun A key or scale in which F is the tonic.
• noun A written or printed note representing this tone.
• noun A string, key, or pipe tuned to the pitch of this tone.
• abbreviation Grammar feminine
• abbreviation focal length
• abbreviation forte
• abbreviation function

from The Century Dictionary.

• noun An abbreviation of Fidei Defensor, Defender of the Faith. See Defender of the Faith, under defender.
• noun An abbreviation of Free Church (of Scotland): as, the F. C. Presbytery.
• noun An abbreviation of field-marshal.
• noun An abbreviation of field-officer.
• noun An abbreviation of Fenian Brother-hood;
• noun of Free Baptist.
• noun An abbreviation in freemasonry, of Fellow-craft;
• noun [lowercase] of the Latin fidei commissum, bequeathed in trust.
• noun An abbreviation of Foreign Mission.
• An abbreviation of fire-plug.
• noun An abbreviation of foot-second.
• The sixth letter and fourth consonant in the English alphabet, as in the Latin and the Phenician, and also as in the early Greek alphabet, through which the Latin was derived from the Phenician (see A), although it has gone out of use in the alphabet generally known to us as Greek.
• In the adaptation of the alphabet to Latin use the sign first received the value we give it, since the f-sound occurred in Latin and needed a representative; the w-sound was provided for by being written with the same character as u. (See U and V.) The sound f, as we pronounce it, is a surd (or breathed, or voiceless) labiodental, a fricative sound or spirant: that is to say, it is made by the audible friction or rustling of the unintonated breath, when forced out between the edge of the lower lip and the tips of the upper teeth, these being held in contact with one another. If, everything else remaining the same, the intonated breath be forced out instead, the sound is v (as in valve, vivid); hence, f and v are corresponding surd and sonant. An f, nearly identical with ours in audible character, may also be made between the edges of the two lips alone, without any help from the teeth; and such a purely labial f is heard in many languages, and is with probability to be regarded as more primitive than the labiodental f, and as forming the transition to it, in the languages where the latter prevails. The same sound is also widely represented in English by ph, but almost only in words coming from the Greek; it also exists in some words written with gh, as laugh, cough, clough, rough, tough, etc., the labial aspirant having taken in such words the place of the palatal, such change being recognized in the spelling in only a few words, as dwarf, draft (= draught), duff (= dough, as formerly pronounced), etc. Historically, f stands in general for a more original p, as found in Sanskrit and the classical languages: thus, father for pitar, πατήρ, pater, etc.
• As a medieval Roman numeral, 40, and with a dash over it, F, 40,000.
• In music: The key-note of the major key of one flat having the signature shown in fig. 3, or of the minor key of four flats having the signature shown in fig. 4; also, the final of the Lydian mode in medieval music.
• In the fixed system of solmization, the fourth tone of the scale of C, called fa, and hence so named by French musicians.
• On the keyboard of the pianoforte, the white key next to the left of each group of three black keys.
• The tone given by such a key, or a tone in unison with such a tone.
• The degree of a staff assigned to such a key or tone; with the treble clef, the lower space or upper line .
• A note on such a degree, indicating such a key or tone .
• [cap. or lowercase] [Abbr. of function.] In algebra, the sign of an operation in general, and especially of a function having a differential coefficient.
• An abbreviation— of Fellow (see F. R. S., F. S. A., etc.);
• in physics, of Fahrenheit (which see);
• in fisheries, of full fish—a commercial mark;
• in a ship's log-book, of fog.
• The chemical symbol of fluorin.
• noun An abbreviation of Foreign Office.

from the GNU version of the Collaborative International Dictionary of English.

• F is the sixth letter of the English alphabet, and a nonvocal consonant. Its form and sound are from the Latin. The Latin borrowed the form from the Greek digamma �, which probably had the value of English w consonant. The form and value of Greek letter came from the Phœnician, the ultimate source being probably Egyptian. Etymologically f is most closely related to p, k, v, and b; as in E. five, Gr. pe`nte; E. wolf, L. lupus, Gr. ly`kos; E. fox, vixen ; fragile, break; fruit, brook, v. t.; E. bear, L. ferre. See Guide to Pronunciation, §§ 178, 179, 188, 198, 230.
• (Mus.) The name of the fourth tone of the model scale, or scale of C. F sharp (F ♯) is a tone intermediate between F and G.
• the bass clef. See under Clef.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The sixth letter of the English alphabet, called ef and written in the Latin script.
• noun The ordinal number sixth, derived from this letter of the English alphabet, called ef and written in the Latin script.
• noun The sixth letter of the basic modern Latin alphabet.
• noun music forte
• noun voiceless labiodental fricative
• noun music The name of the fourth tone of the model scale, or scale of C. F sharp (F♯) is a tone intermediate between F and G.