The letter X

X /X/ n. 1. Used in various speech and writing contexts (also
XEROX PARC /zee'roks park'/ The famed Palo Alto Research
XOFF /X-of/ n. Syn. control-S.
XON /X-on/ n. Syn. control-Q.
xor /X'or/, /kzor/ conj. Exclusive or. `A xor B' means
xref /X'ref/ vt., n. Hackish standard abbreviation for
XXX /X-X-X/ n. A marker that attention is needed.
xyzzy /X-Y-Z-Z-Y/, /X-Y-ziz'ee/, /ziz'ee/, or /ik-ziz'ee/