What is the meaning of Capillary?

Resembling or pertaining to hair, especially in slenderness or fineness.

Of or pertaining to a narrow tube.

Of, relating to, or caused by surface tension.

Of or relating to capillaries in the body or to capillary action.

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).

A tube or channel having a very small internal diameter, through which liquid can rise or be drawn by capillary action.

Source: wiktionary.org