noun
long-service employee; veteran worker
Refers to a person who has worked continuously for the same employer for many years. Often used in corporate or institutional contexts.
彼は30年の勤続者として表彰された。
He was recognized as a 30-year long-service employee.
古参 emphasizes seniority or being an old-timer in a group, not necessarily continuous service with one employer.
Compound of 勤続 (continuous service) + 者 (person). The exact historical derivation is straightforward; the word is a modern formation.