self-raising flour vs premix

self-raising flour and premix both are nouns.

Word	Noun	Adjective	Verb	Adverb
self-raising flour	Yes	No	No	No
premix	Yes	No	No	No

As nouns, premix is a hypernym of self-raising flour; that is, premix is a word with a broader meaning than self-raising flour:

self-raising flour: a commercially prepared mixture of flour and salt and a leavening agent
premix: a commercially prepared mixture of dry ingredients

Other hypernyms of self-raising flour include mix.

self-raising flour (noun)	premix (noun)
a commercially prepared mixture of flour and salt and a leavening agent	a commercially prepared mixture of dry ingredients