In anatomy|lang=en terms the difference between alveolus and capillary
is that
alveolus is (anatomy) a small air sac in the lungs, where oxygen and carbon dioxide are exchanged with the blood while
capillary is (anatomy) any of the small blood vessels that connect arteries to veins.
As nouns the difference between alveolus and capillary
is that
alveolus is a small cavity or pit while
capillary is a narrow tube.
As an adjective capillary is
of or pertaining to hair.