The combining of two words:
lyric: "having a pleasing succession of sounds"
-osis: "a disorder or abnormal state"
to mean when a person is singing and doesn't know or forgets the words to a song so they proceed to make up sounds and grunts to cover the fact that they sound like an idiot.
My sister and I got drunk last night and were singing Billy Jean loudly when I realized the bitch was suffering from lyricosis, she had no idea what the words were.
I love laughing at that dude that always sings for Karaoke even though he has such a severe case of lyricosis.
I don't care if I don't know the words to the song, a little lyricosis usually hides the mistakes.