membrum

Membrum, membri, n., is second declension. Two senses run in parallel from the start: a limb of the body, and a component of any structured whole - a member of a household, a section of a law, a clause of a sentence, which is what the rhetoricians mean by membrum when they are translating the Greek kolon.

Paul makes the second sense theological, the faithful as membra of one corpus, and medieval Latin runs with it. Watch the plural: membra used on its own, especially in poetry, regularly means the whole body rather than the arms and legs specifically, so membra lavare is to wash yourself. Dismembrare, "pull the limbs off", gives English "dismember", and membrana, a skin or parchment, gives "membrane".