The compound adjective 'three-member' is a transparent and relatively modern formation in English, built by directly combining the native number 'three' with the noun 'member'. The word 'three' has a stable lineage from Proto-Indo-European tréyes, descending into the Germanic branch as the cardinal number. 'Member' has a more complex journey, originating from the Proto-Indo-European root memso- meaning 'flesh, meat', which evolved in Latin to membrum specifically denoting a limb or part of the body. This anatomical sense was metaphorically extended in medieval Latin and Old French to mean a constituent part of a collective body, such as a society or committee, which is the meaning absorbed into Middle and Modern English. Thus, the logic of 'three-member' is straightforwardly arithmetic: it literally denotes a unit composed of three constituent parts or persons, applying the classical part-whole metaphor inherent in 'member' to a quantified structure.

Structure: three (number) + member (constituent part) - three: From Old English þrīe, þrēo, of Germanic origin; related to Dutch drie and German drei, from an Indo-European root shared by Latin tres and Greek treis. Functions as a numerical quantifier. - member: From Old English lim, related to Old Norse limr. The modern sense of 'a person belonging to a group' developed in Middle English from the notion of a limb as a part of the body, influenced by Old French membre and Latin membrum ('limb, part of the body'). Functions as the noun being quantified.