prefix used for CCITT-ratified (UN) international telecom standards on e-mail

plural of X

plural of x

plural of X chromosome

plural of X-Phile

plural of x-height

(typography) The distance between the baseline and midline in a typeface, typically equal to the height of the lower-case letter x.

(informal, usually used attributively) cross-country / (informal) cross-country skiing

Across the country.

(transitive) To cross out with a series of the letter X, or with scribbles or lines. / (computing) To close a window (typically by clicking a button marked with an X symbol).