x

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The 24th letter of the modern English alphabet.
2. n. Any of the speech sounds represented by the letter x.
3. n. The 24th in a series.
4. n. Something shaped like the letter X.
5. n. A mark inscribed to represent the signature of one who is unable to sign one's name.
6. n. An unknown or unnamed factor, thing, or person.
7. v. To mark or sign with an X.
8. v. To delete, cancel, or obliterate with a series of X's. Often used with out.
9. The symbol for abscissa.

Century Dictionary and Cyclopedia

1. The chemical symbol of xenon.
2. In electricity, the symbol for reactance in alternating-current circuits.
3. In wireless telegraphy, a local disturbance causing a false signal; a stray.
4. The twenty-fourth letter and nineteenth consonant-sign in the English alphabet. In the Latin alphabet, from which it comes to ours, it followed next after U or V (which were then only one letter: see U), and was till a late date the last letter in that alphabet, till Y and Z (see those letters) were finally added from the Greek to represent peculiar Greek sounds. The sign X was a Greek addition to the Phenician alphabet; it had in early Greek use a divided value: in the eastern alphabets, that of kh (besides the signs for ph and th); in the western, that of ks (besides the signs for ps and ts or ds). The former of the two came afterward to be the universally accepted value in Greece itself; while the latter was carried over into Italy, and so became Roman, and was passed on to us. Hence our X has in general the Latin value ks; but as initial (almost only in words from the Greek, and there representing a different Greek character, the ksi) we have reduced it to the z-sound, as in Xerxes, xanthous. In many words also, especially among those beginning with ex, it is made sonant, or pronounced as gz. The accepted rule for this is that the gz- sound is given after an unaccented before an accented vowel, as in exért, exilic (egzert, egzilic), over against éxercise, éxile (eksercize, eksīl). But usage does not follow the rule with exactness, and many cultivated speakers disregard the distinction altogether, pronouncing everywhere alike ks (or kz). In any case, the sign X is superfluous in English, as it was in Latin and in Greek; it denotes no sound which is not fully provided for otherwise. In Old English it was sometimes used for sh, as in xal = shall.
5. As a numeral, X stands for ten. When laid horizontally (), it stands for a thousand, and with a dash over it (), it stands for ten thousand.
6. As an abbreviation, X. stands for Christ, as in Xn. (Christian), Xmas. (Christmas).
7. As a symbol: In ornithology, in myological formulas, the symbol of the semitendinosus muscle.
8. In mathematics:
9. [lowercase] In algebra, the first of the unknown quantities or variables.
10. [l. c] In analytical geometry, an abscissa or other rectilinear point-coördinate.
11. In mechanics, the component of a force in the direction of the axis of x.
12. Originally, a mark on brewers' casks; hence, a name given to ale of a certain quality. Compare XX, XXX.

Wiktionary

1. n. The twenty-fourth letter of the basic modern Latin alphabet.
2. n. voiceless velar fricative.
3. n. mathematics An unknown variable.
4. n. mathematics The first coordinate in Cartesian coordinates, representing horizontal position.
5. n. A kiss at the end of a letter, or similar missive.
6. n. The twenty-fourth letter of the English alphabet, called ex and written in the Latin script.

GNU Webster's 1913

1. X, the twenty-fourth letter of the English alphabet, has three sounds; a compound nonvocal sound (that of ks), as in wax; a compound vocal sound (that of gz), as in example; and, at the beginning of a word, a simple vocal sound (that of z), as in xanthic. See Guide to Pronunciation, §§ 217, 270, 271.

WordNet 3.0

1. n. the cardinal number that is the sum of nine and one; the base of the decimal system
2. n. street names for methylenedioxymethamphetamine
3. adj. being one more than nine
4. n. the 24th letter of the Roman alphabet