means A vein is a blood vessel that carries blood back toward the heart, though the word also stretches to mean a streak of mineral in rock, a mood or style of expression, or a thin branching line in a leaf or insect wing.

from From Latin 'vena,' meaning a blood vessel or, by extension, a streak in stone or wood — the Romans already saw the metaphor running through the body, the earth, and the timber. It traveled into English through Old French 'veine.' The mineral and metaphorical senses ('a vein of gold,' 'in a lighter vein') were carried along inside the word from the very start, riding the same channel.