This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

n. A set contained within a set.

n. With respect to another set, a set such that each of its elements is also an element of the other set.

n. A group of things or people, all of which are in a specified larger group.

n. In mathematics, a proper part or the whole of the set: thus, a subset of S is a set every element of which belongs to S.

n. a set whose members are members of another set; a set contained within another set

"Indeed, the bigger point to be made is that empiricism is all that we have to explain anything that we wish to understand, “physics” being only what we call a subset of empirically-based theories."

set   

⊆    ⊂   

phenotype    anergy    subtypes    recruitment    proliferation    differentiation    precursor    lineage    lymphocytes    progenitor