(organic chemistry) A group of about twenty closely related compounds obtained from the dried latex that exudes from the seed capsule of the opium poppy Papaver somniferum.

morphine alkaloid

(chemistry) any of a range of related alkaloids found in various species of the genus Nicotiana, especially Nicotiana tabacum which is cultivated for the manufacture of cigarettes

(archaic) A ptomaine.

(organic chemistry) Any of various alkaloids of similar chemical structure, including harmine, harmaline, and harmalol, that function as MAOIs and are found in the seeds of Peganum harmala.