ready-mix vs cake mix

ready-mix and cake mix both are nouns.

Word	Noun	Adjective	Verb	Adverb
ready-mix	Yes	No	No	No
cake mix	Yes	No	No	No

As nouns, cake mix is a hyponym of ready-mix; that is, cake mix is a word with a more specific, narrower meaning than ready-mix:

ready-mix: a commercial preparation containing most of the ingredients for a dish
cake mix: a commercial mix for making a cake

Other hyponyms of ready-mix include brownie mix, lemonade mix.

ready-mix (noun)	cake mix (noun)
a commercial preparation containing most of the ingredients for a dish	a commercial mix for making a cake