What is the word for this?

Hi,

I'm wondering what the word (if there is one) for what happens when, in a list, description x contains z, rendering any additional mention of z redundant. Example: "I went out to buy ski gear and ski boots." Since ski boots would generally be regarded as a type of ski gear, including it is tautological. But what is the word for what happens here? The closest I've come is that ski gear supersedes ski boots, but surely there must be a better word for it.

Any help is appreciated.