(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).

5-bromo-4-chloro-3-indolyl-β-D-galactopyranoside, used to detect β-galactosidase.

plural of x-ray

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

Across the country.

Abbreviation of moto-cross.

(grammar, X-bar theory) A phrase, or, equivalently, a node in a syntax tree, which consists either of: (1) an adjunct and another X-bar phrase, (2) a head, X, and an optional complement, or (3) a conjunction sandwiched between two other X-bars. The X is a "pro-letter" which can be substituted by letters such as N for noun, V for verb, P for preposition, I for inflectional, etc.

Unix-like operating system (e.g., Linux, macOS, Solaris, etc.).

Alternative spelling of X-ray

Alternative letter-case form of X-ray