Apart means separated by distance, time, or difference, or not together.
From Old French "à part" meaning "to the side" or "separately." The pieces "a" (to) and "part" (piece or portion) literally describe something moved to its own side.
“Apart” and “a part” are opposites separated by a tiny space: one means separated, the other means included. A single space flips the meaning from distance to belonging.
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