an attack in which an army surrounds a castle or city in order to prevent the people inside from receiving food and waterThe troops prepared to withstand a long siege.
break a siege (=to cause a siege to end): An attempt was made to break the 38-month siege of Sarajevo.
lift/raise a siege (=to end a siege): The king lifted the siege two months later.
under siege (=in a siege): Malta was under siege in World War II.