dex·tro·me·thor·phan \ˌdekstrōmə̇ˈthȯrˌfan\noun (-s) Etymology:dextr- + methyl + morphinan parent substance of morphine alkaloids, from morphine + -an (III) : a nonaddicting cough suppressant C18H25NO that is widely used especially in the form of its hydrobromide in over-the-counter cough and cold preparations