紀元

1. Origins, structure, and basic meaning

• Structure: 紀元 is read as きげん and is a noun for the epoch or starting point from which years in a chronology are counted.
• Basic usage: Use 建国の年を紀元とする for choosing a base year and 新しい紀元が定められる for establishing a new epoch.

2. Common pitfalls and similar expressions

• Difference from 元年
  • 元年 is the first year of an era name or period; 紀元 is the reference point for an entire chronological system.
• Not a cause in this sense
  • Here the word means the beginning used for dating, not a general cause or origin of an event.