Extension is a term that describes the act of extending something or making it longer, broader, or bigger. Its antonyms, therefore, refer to words that describe actions that are the opposite of extension. These could include terms such as reduction, contraction, shrinkage, compression, or constricting. For instance, if you were discussing a budget proposal, you might talk about the need to reduce the budget rather than extend it. Similarly, in architecture, a plan may call for the contraction or compression of a particular structure to fit within a certain footprint. The use of antonyms is a useful way to convey a clear opposite meaning to a particular term.