capillary

adj

1. Resembling or pertaining to hair, especially in slenderness or fineness.
2. Of or pertaining to a narrow tube.
3. Of, relating to, or caused by surface tension.
4. Of or relating to capillaries in the body or to capillary action.

noun

1. Any of the small blood vessels (from 5 to 10 micrometres/micrometers (μm) in diameter) that connect arteries to veins (They are the smallest blood vessels in the body: they convey blood between the arterioles and venules).
2. A tube or channel having a very small internal diameter, through which liquid can rise or be drawn by capillary action.