concrete – n. a hard substance used in building

implication – n. a result or effect

delta – n. a low, flat area of land where a river divides into smaller rivers and goes into the sea

alternative – n. one of two or more things to choose between

vanish – v. disappear

fortress – n. a castle or other strong building built to defend a place

foundation – n. the part of a building that sits under the ground to support it