Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
somnĭfĭcus, a, um, adj. [somnus-facio], causing sleep, narcotic (Plinian): crater, Mart. Cap. 1, § 82: medicamentum, Plin. 37, 10, 57, § 158: vis aspidum, id. 24, 4, 17, § 63.