enormous, immense, huge, vast, gigantic, colossal, mammoth mean exceedingly large.

enormous and immense both suggest an exceeding of all ordinary bounds in size or amount or degree, but enormous often adds an implication of abnormality or monstrousness.

huge commonly suggests an immensity of bulk or amount.

vast usually suggests immensity of extent.

gigantic stresses the contrast with the size of others of the same kind.

colossal applies especially to a human creation of stupendous or incredible dimensions.

mammoth suggests both hugeness and ponderousness of bulk.