Chiliad is a relatively obscure word that refers to a period of 1,000 years. However, there are a number of synonyms that can be used in place of chiliad. These include millennium, which is perhaps the most commonly used substitute. Other options include kiloyear, grand, and eon. However, these words are less commonly used in everyday language and may be unfamiliar to many readers. Overall, while chiliad has a certain charm to it, it's important to have a variety of alternative words to choose from when writing or speaking.