1. The state or quality of being higher in a position; priority by reason of birth, a superior age: Because the prince had seniority over his younger brother, the duke, the prince assumed responsibility for drafting the new laws.
2. Priority or precedence in office or service; especially military: Susan's seniority at the company allowed her to have three weeks annual vacation.
3. Superiority in standing to another of equal rank by reason of earlier entrance into the service, or an earlier date of appointment: Mr. Johnson, the elderly politician, had seniority over the more recently elected representatives.