The word "extensities" is not a commonly used term and it does not have any established synonyms. However, one can consider alternatives words like "extent," "breadth," "range," "scope," or "magnitude," which convey a similar meaning to "extensities." These words emphasize the extent or scope of something, indicating a large or comprehensive range. "Extensities" can also be replaced by "size," "dimension," or "measurement," which indicate the physical or numerical extent of something. Using these alternatives words can make your speech or writing more precise and effective, providing a clear understanding of the extent or magnitude of something.