end-member \ˈ ̷ ̷ˌ ̷ ̷ ̷ ̷\noun : a pure chemical compound in some cases hypothetical but regarded as a component entering into solid solution with other pure chemical compounds to form an isomorphous series of minerals < fayalite Fe2SiO4 and forsterite Mg2SiO4 are end-members of the olivine series (Mg,Fe)2SiO4 >