定期

1. Origins, structure, and basic meaning

• Structure: 定期(ていき) indicates recurrence at a fixed period or interval and, in context, can be short for a commuter pass.
• Basic usage: For a repeating schedule it appears in 定期点検; for a transit pass it appears in 三か月の定期を買う.

2. Common pitfalls and similar expressions

• Distinguish modifier and noun uses
  • In 定期点検 it means “regular” or “periodic,” while by itself in a transit context it can refer to 定期券.
• Difference from 定期券
  • 定期券(ていきけん) is the full term for a commuter or season pass, while 定期 can be its shortened form or mean “periodic.”