xyzzy: /X-Y-Z-Z-Y/, /X-Y-ziz'ee/, /ziz'ee/, or /ik-ziz'ee/ [from the ADVENT game] adj.

:xyzzy: /X-Y-Z-Z-Y/, /X-Y-ziz'ee/, /ziz'ee/, or /ik-ziz'ee/
[from the ADVENT game] adj. The {canonical} `magic word'.
This comes from {ADVENT}, in which the idea is to explore an
underground cave with many rooms and to collect the treasures you
find there. If you type `xyzzy' at the appropriate time, you can
move instantly between two otherwise distant points. If,
therefore, you encounter some bit of {magic}, you might remark
on this quite succinctly by saying simply "Xyzzy!" "Ordinarily
you can't look at someone else's screen if he has protected it, but
if you type quadruple-bucky-clear the system will let you do it
anyway." "Xyzzy!" Xyzzy has actually been implemented as an
undocumented no-op command on several OSes; in Data General's
AOS/VS, for example, it would typically respond "Nothing
happens", just as {ADVENT} did if the magic was invoked at the
wrong spot or before a player had performed the action that enabled
the word. In more recent 32-bit versions, by the way, AOS/VS
responds "Twice as much happens". See also {plugh}.
-- The AI Hackers Dictionary