triweekly definitions

Merriam Webster's

I. adjective Date: 1832 1. occurring or appearing three times a week 2. occurring or appearing every three weeks • triweekly adverb II. noun (plural -lies) Date: 1838 a triweekly publication

Webster's 1913 Dictionary

Triweekly 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. 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.