Tri"week`ly (?), a. [Pref. tri- + weekly.]
Occurring or appearing three times a week; thriceweekly; as, a triweekly newspaper.
--
adv.
Three times a week.
--
n.
A triweekly publication.
⇒ 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.
© Webster 1913.