member (n.)

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.

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Definitions of member

member (n.)
one of the persons who compose a social group (especially individuals who have joined and participate in a group organization);
only members will be admitted
she was introduced to all the members of his family
a member of the faculty
Synonyms: fellow member
member (n.)
anything that belongs to a set or class;
members of the opposite sex
snakes are members of the class Reptilia
member (n.)
an external body part that projects from the body;
Synonyms: extremity / appendage
member (n.)
an organization that is a member of another organization (especially a state that belongs to a group of nations);
Canada is a member of the United Nations
the library was a member of the interlibrary loan association
member (n.)
the male sex organ (`member' is a euphemism);
Synonyms: penis / phallus