Quinquennia refers to a period of five years, and there are several synonyms for this term, including quinquennium, lustrum, and pentad. Quinquennium is derived from the Latin word 'quinquennium,' and it is frequently used in academic and historical contexts. Lustrum is another synonym for quinquennia, which is also derived from Latin, and it refers to a five-year period in ancient Rome. Additionally, pentad is a less commonly used synonym for quinquennia, which stems from the Greek word 'pentad,' meaning 'a group of five things.' All of these terms can be used to describe a period of five years, and they are often interchangeable in their usage.