Capillary
A very narrow diameter tube, e.g. as fine as a hair, in which the surface tension forces exert a measurable effect on a liquid.
Capillary action
Effect due to the forces of surface tension which are exerted in very fine tubes. For example, when a capillary tube is plunged in a tank containing a liquid, the height of liquid in the tube rises to a height which is much larger than for a tube with larger diameter.