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1.
A substance which puts one to sleep.
This tea is very somniferous, it makes my eyes tired drinking it.
by niblicator March 10, 2009
 
2.
A small flightless found in the outer regions of Canada and western Russia. Renowned for it's amazing renditions of 'If you wanna be my lover' which can put one to sleep.
Also, a berk.
Gay Journey is somniferous
by Gay Journey September 24, 2008