pudding vs plum pudding

pudding and plum pudding both are nouns.

Word	Noun	Adjective	Verb	Adverb
pudding	Yes	No	No	No
plum pudding	Yes	No	No	No

As nouns, plum pudding is a hyponym of pudding; that is, plum pudding is a word with a more specific, narrower meaning than pudding:

pudding: any of various soft sweet desserts thickened usually with flour and baked or boiled or steamed
plum pudding: a rich steamed or boiled pudding that resembles cake

pudding (noun)	plum pudding (noun)
any of various soft sweet desserts thickened usually with flour and baked or boiled or steamed	a rich steamed or boiled pudding that resembles cake
any of various soft thick unsweetened baked dishes
(British) the dessert course of a meal (`pud' is used informally)