What is Fhtagn?
1.
A crucial part of the chant which calls forth the attention of
"Ph'nglui mglw'nafh
Cthulhu R'lyeh wgah'nagl fhtagn!"
2.
Part of a phrase in HP Lovecraft's
The phrase - Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn - translates to, "In his house at R'lyeh, dead Cthulhu waits dreaming."
It is often shortened to, "Cthulhu fhtagn," which loosely translates to, "Cthulhu waits," or "Cthulhu dreams."
"Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn."
-HP Lovecraft's Call of Cthulhu
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3.
Word which roughly translates to waits/dreams/sleeps in a long forgotten tongue.
"Iä! Iä! Cthulhu fhtagn!" Rejoice that Cthulhu sleeps.
See