non-member n.

a prefix used freely in English and meaning "not, lack of," or "sham," giving a negative sense to any word, 14c., from Anglo-French noun-, from Old French non-, from Latin non "not, by no means, not at all, not a," from Old Latin noenum "not one" (*ne oinom, from PIE root *ne- "not" + PIE root *oi-no- "one, unique"). In some cases perhaps from Middle English non "not" (adj.), from Old English nan (see not). "It differs from un- in that it denotes mere negation or absence of the thing or quality, while un- often denotes the opposite of the thing or quality" [Century Dictionary].

c. 1300, "body part or organ, an integral part of an animal body having a distinct function" (in plural, "the body"), from Old French membre "part, portion; topic, subject; limb, member of the body; member" (of a group, etc.)," 11c., from Latin membrum "limb, member of the body, part," probably from PIE *mems-ro, from root *mems- "flesh, meat" (source also of Sanskrit mamsam "flesh;" Greek meninx "membrane," mēros "thigh" (the "fleshy part"); Gothic mimz "flesh").

In common use, "one of the limbs or extremities." Especially "the sex organ" (c. 1300, compare Latin membrum virile, but in English originally of women as well as men). Figurative sense of "anything likened to a part of the body" is by 14c., hence "a component part of any aggregate or whole, constituent part of a complex structure, one of a number of associated parts or entities."

The transferred sense of "person belonging to a group" is attested from mid-14c., from notion of "person considered in relation to an aggregate of individuals to which he or she belongs," especially one who has united with or been formally chosen as a corporate part of an association or public body. This meaning was reinforced by, if not directly from, the use of member in Christian theology and discourse from mid-14c. for "a Christian" (a "member" of the Church as the "Body of Christ"). Meaning "one who has been elected to parliament" is from early 15c.