What does "triweekly" mean?

Triweekly: Occurring or appearing three times a week; thriceweekly; as, a triweekly newspaper. -- adv. Three times a week. -- n. A triweekly publication. Note: This is a convenient word, but is not legitimately formed. It should mean occurring once in three weeks, as triennial means once in three years. Cf. Biweekly.