ves·i·cle 
(vĕsĭ-kəl)
(vĕsĭ-kəl)n.
A small enclosed structure or cavity, especially:
a. Cytology A membrane-bound structure within a cell in which materials such as enzymes are transported or stored.
b. Anatomy A sac or cyst, especially one containing fluid.
c. Medicine A blister of the skin.
d. Geology A cavity formed in volcanic rock by entrapment of a gas bubble during solidification.
[Middle English, from Old French vesicule, from Latin vēsīcula, diminutive of vēsīca, bladder, blister.]