Abarim Publications' online Biblical Greek Dictionary
The noun μελος (melos) means member, but specifically a member of an assemblage that operates in synchronicity or harmony. It's the root of our word "melody", which stems from the noun μελωδια (melodia), chant or choral song, hence also the adjective μελωδης (melodes), consisting of members.
Our word "choir" actually stems from the verb χαιρω (chairo), meaning to rejoice (hence English words like charity and charisma), which in turn stems from the Proto-Indo-European root gher-, which has to do with collectivity and enclosures: hence words like carol, choir, chorus, cohort, court and the familiar Latin word hortus, meaning garden. All this is significant because the noun μηλον (melon) means apple or any kind of fruit from a tree, while the identical noun μηλον (melon) means sheep or goat. These two nouns have their parent verb in common, namely μελω (melo), meaning to be an object of care.
Our noun μελος (melos), meaning member, occurs 34 times in the New Testament, see full concordance, and always denotes bodily members. This indicates that to the ancients, the body was not a robotic assemblage of independent parts but rather a choir that sings a harmonious song (also see our article on the Hebrew noun בשר, basar, meaning flesh or "glad tidings"). Quite literally, the Body of Christ is a collective of human individuals who interact as harmonious as physical organs do in an individual organic body.
Tellingly, our noun has no derivatives.