vesicle

rakko, vesirakkula, rakkula puhekieltä A membrane-bound compartment found in a cell.
A small bladder-like cell or cavity.
puhekieltä A small sac or cyst or vacuole, especially one containing fluid. A blister formed in or beneath the skin, containing serum. A bleb.
puhekieltä A pocket of embryonic tissue that is the beginning of an organ.
puhekieltä A small cavity formed in volcanic rock by entrapment of a gas bubble during solidification.
2004, (w), The Earth, Folio Society 2011, p. 51:

It frequently contains holes, or vesicles, especially nearer the surface of a flow where gas has escaped.