(N.) A monster in Final Fantasy XI that has special restrictions to how it spawns. These restrictions can either be a time limit or a forced spawn, to force the monster to appear by baiting it out. Notorious monsters almost always have unique names and are more powerful then the other monsters around. Notorious monsters often reward you with special or expensive items uppon defeating them.
Joe: OMG I just killed the notorious monster I've been trying to kill for 3 months! :D
Jay: Everyone ready?
Other people: YEAH!
Jay: ok, spawn the NM.