1. experimental.
2. extra.
3. extraordinary.
Symbol.
1. the 24th in order or in a series, or, when I is omitted, the 23rd.
2. ( sometimes l.c. ) the Roman numeral for 10. Cf. Roman numerals .
3. Christ.
4. Christian.
5. cross.
6. Elect. reactance.
7. Slang. a ten-dollar bill.
8. (in the U.S.) a rating of the Motion Picture Association of America for movies with subject matter that is suitable for adults only: persons who are under age (usually 17) will not be admitted. Cf. G (def. 7), PG, PG-13, R (def. 5).
9. (in Great Britain) a designation for a film recommended for adults only. Cf. A (def. 11), AA (def. 5), U (def. 5).
10. a person, thing, agency, factor, etc., of unknown identity.
11. Chem. (formerly) xenon.