somnific vs soporific

somnific is not a noun while soporific is a noun.

Word	Noun	Adjective	Verb	Adverb
somnific	No	Yes	No	No
soporific	Yes	Yes	No	No

As adjectives, somnific and soporific are synonyms defined as:

Other synonyms of somnific include hypnagogic, hypnogogic, somniferous, soporiferous.

somnific (noun)	soporific (noun)
	a drug that induces sleep

somnific (adjective)	soporific (adjective)
sleep inducing	sleep inducing
	inducing mental lethargy