denoting the next after W in a set of items, categories, etc..
denoting an unknown or unspecified person or thing:there is nothing in the data to tell us whether X causes Y or Y causes X
(x) (in describing play in bridge) denoting an unspecified card other than an honour:East knows that declarer cannot hold a doubleton Qx
(usually x) the first unknown quantity in an algebraic expression, usually the independent variable.
[the introduction of x, y, and z as symbols of unknown quantities is due to Descartes (Géométrie, 1637), who took z as the first unknown and then proceeded backwards in the alphabet]
(usually x) denoting the principal or horizontal axis in a system of coordinates: [in combination]:the x-axis
2a shape like that of a letter X:two wires in the form of an X [in combination]:an X-shaped cross
3a cross-shaped written symbol, in particular:
used to indicate a position on a map or diagram:put an X on the spot where you think its eye should be
used to indicate a mistake or incorrect answer.
used in a letter or message to symbolize a kiss.
used to indicate one’s vote on a ballot paper:with trembling hand you inscribe your X on the slip of paper
used in place of the signature of a person who cannot write:nearly all those engaged in the fur trade signed with an X