Blister, blood
A blister full of blood due to a pinch, bruise or repeated friction.</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.