Water blister

A blister with clear watery contents that is not purulent (does not contain pus) and is not sanguineous (does not contain blood).</P> A blister is medically termed a vesicle.

One that is more than 5 mm in diameter with thin walls and is full of watery fluid is called a bulla or a bleb.</P> The word 'blister' entered English in the 14th century.

It came from the Middle Dutch 'bluyster', blister and was a modification of the Old French 'blostre' which meant a leprous nodule -- a rise in the skin due to leprosy.