Of a motion picture; of such a nature that admission is denied to persons under a specified age (as 17) — used before the adoption of NC-17

Roman numeral ten; a person or thing unknown.

The 24th letter of the English alphabet, with a sound that can be represented medially by ks and initially by z. It is derived through Latin from the alphabet of W Greece, and was the last letter in the earlier Latin alphabet.

In mathematics, an unknown quantity.