What is Vein ?
Vein is (noun) 1. a small tube in the body which takes blood from the tissues back to the heart The veins in her legs are swollen. 2. a mood shown in speaking or writing He went on in the same vein for twenty minutes. in poetic vein feeling poetic 3. a thin tube forming part of the structure of a leaf The veins are easily seen if you hold the leaf up to the light. 4. a thin layer of mineral in rock They struck a vein of gold. (NOTE: Do not confuse with vain.)
source: Easier English, Student Dictionary Upper Intermediate Level