Oligodendrocyte
A type of cell in the central nervous system.
The oligodendrocytes surround and insulate the long fibers (the axons) through which the nerves send their electrical messages.
The term 'oligodendrocyte' comes from the fact that through a microscope the cell's projections looked like the sparse branches of a tree.
The word is from the Greek 'oligo-', few or scant + 'dendron', tree + '-cyte', cell.