Contraction of "fuck" and nah (being synonymous with "no") to form a emphasized statement of disagreement or answer to a query. Similar to saying "fuck no" but phonetically abbreviated.
by niok chang September 18, 2006
 Get the fnahmug.
Get the fnahmug. "Most ways of indirectly opening the PHP script would allow you to view it's contents. Maybe bofing the server would make it stop parsing, but don't take my word for it."
"Fnah."
(See bof, boff.)
"Fnah."
(See bof, boff.)
by Henry Kissinger December 12, 2004
 Get the fnahmug.
Get the fnahmug.