Vesicle

noun

1. A membrane-bound compartment found in a cell.
2. A small bladder-like cell or cavity; a vesicula.
3. A small sac or cyst or vacuole, especially one containing fluid. A blister formed in or beneath the skin, containing serum. A bleb.
4. A pocket of embryonic tissue that is the beginning of an organ.
5. A small cavity formed in volcanic rock by entrapment of a gas bubble during solidification.