1. Marks the spot on treasure maps.
2. Greek letter Chi.
3. Multiplication sign, also the vector cross product symbol.
4. As a mark, means either 'yes' or 'no'.
5. Signature of an illiterate person.
6. Marks clothing as both bigger and smaller: XXS or XXL.
7. Greek numeral for 600.
8. The Roman numeral for 10.
9. Mathematical symbol for unknown or changing concepts.
10. In astronomy, a comet of unknown orbit.
11. In electronics, reactance.
12. X-band: part of the microwave band of the electromagnetic spectrum.
13. Hobo sign: don't knock here.
14. X chromosome: having just one is good, two...watch out.
15. Planet X, a hypothesised planet in the outer solar system.
16. Conserved quantum number in particle physics.
17. Rating given to films suitable for an adult-only audience
18. Written symbol of a kiss.
19. Symbol in the International Phonetic Alphabet for voiceless velar fricative.
20. Stock symbol for United States Steel Corporation.
21. Street names for the drug MDMA, ecstasy.
22. Symbol for a strike in bowling.
23. Straight edgers symbol to show committment to their lifestyle.
24. Embellishes online nicknames of girls who crave attention.
25. Abbreviation of extreme: X-Games.
26. Unnecessary letter, "z" and "cks" already exist.
27. Henry Miller's "mysterious element X" which makes creative people interesting.
28. Archnemesis of O in Tic-Tac-Toe.
29. Mark on a scholastic examination: "Wrong answer!"
30. Written across the hand of someone who is under drinking age in a bar.
31. Slang for "Christ": Xmas.
32. On a map: "You are here."
33. Anima mundi: the bands which form the soul of the world form an X.
34. One-third porn.
35. Used in the names of rock radio stations that repeat the same songs endlessly.
36. The last part of sex.
37. Along with the letter O, reads correctly upside down or backwards.
38. Slang for "cross": Santa Cruz translates to Holy Cross.
39. In chess transcription: takes piece.
40. In marketing: added to product names when actual improvements cost too much.
41. Egyptian hieroglyph it meant to damage, divide, count, or break into parts.
42. 24th letter in the basic modern Latin alphabet.
42 meanings, what a remarkable coincidence.
Photo: X Tee Shirt Logo/Matt Seidenzahl, Silkscreen Express, firstname.lastname@example.org