triennialtri‧en‧ni‧al /traɪˈeniəl/ adjective 
Word Origin
Word OriginWORD ORIGINtriennial
ExamplesOrigin:
1500-1600 Latin triennis, from triennium ‘three years’, from tri- + annus ‘year’EXAMPLES FROM THE CORPUS
word sets- At their triennial congress on Sept. 15-21, 1990, delegates adopted a new party programme replacing that of 1975.
- June 30 would mark the end of the triennial contract cycle that had punctuated labor-management relations in the copper industry since midcentury.
- The triennial election for the Senate Presidency took place on Oct. 2.
- The Fourth Lateran Council, held at the end of his reign, imposed a triennial twentieth for the same purpose.
WORD SETS► Chronology
happening every three years → annualAD, advance, verbafter, prepositionafternoon, nounalarm, nounalarm clock, nouna.m., Anno Domini, annual, adjectiveApril, nounAsh Wednesday, nounAug., August, nounautumn, nounautumnal, adjectivebank holiday, nounBC, BCE, biannual, adjectivebicentenary, nounbicentennial, nounbiennial, adjectivebimonthly, adjectivebirthday, nounbiweekly, adjectivebonfire night, nounBoxing Day, nounBritish Summer Time, nounBST, nouncalendar, nouncalendar month, nouncalendar year, nouncarriage clock, nouncentenary, nouncentury, nounChristmas, nounChristmas Day, nounChristmas Eve, nounChristmastime, nounchronograph, nounchronological, adjectivechronometer, nouncircadian, adjectiveclock, nouncrystal, nouncuckoo clock, nouncycle, nouncyclic, adjectivedaily, adjectivedaily, adverbdate, noundate, verbdawn, nounday, nounDec., decade, nounDecember, noundiamond anniversary, noundiamond jubilee, noundinnertime, noundiurnal, adjectived.o.b., due date, noundusk, nounface, nounFather's Day, nounfeast, nounFebruary, nounfortnightly, adjectiveFourth of July, the, Fri., Friday, nounGood Friday, nounGreenwich Mean Time, nounGregorian calendar, nounguy, nounGuy Fawkes Night, nounhalf-hourly, adjectivehalf-yearly, adjectiveHalloween, nounhand, nounHanukkah, nounharvest festival, nounHogmanay, nounhorn, nounhour, nounhourglass, nounhour hand, nounhr, Independence Day, nounJan., January, nounjubilee, nounJuly, nounJune, nounLabor Day, nounleap year, nounlunar month, nounmainspring, nounman-hour, nounMar., March, nounMardi Gras, nounmarket day, nounMaundy Thursday, nounMay, nounMay Day, nounMichaelmas, nounmidday, nounmiddle age, nounmiddle-aged, adjectivemidnight, nounMidsummer Day, nounmidweek, adjectivemillennium, nounmin., minute hand, nounMon., Monday, nounmonth, nounmorn, nounmorning, nounMothering Sunday, nounMother's Day, nounmovable feast, nounnew moon, nounNew Year, nounNew Year's Day, nounNew Year's Eve, nounnight, nounnightfall, nounnighttime, nounnocturnal, adjectiveNoel, nounnoon, nounnoonday, adjectiveNov., November, nounOct., October, nounp.a., Pancake Day, nounPDT, penultimate, adjectiveper annum, adverbper diem, adverbperiodic, adjectivep.m., PST, public holiday, nounquarter, nounquotidian, adjectiveRemembrance Day, nounSat., Saturday, nounschoolday, nounseason, nounsecond, nounsecond hand, nounself-winding, adjectiveSeptember, nounshockproof, adjectivesilver anniversary, nounsilver jubilee, nounsilver wedding anniversary, nounsolar year, nounsolstice, nounspring, nounspringtime, nounstandard time, nounstopwatch, nounsummer, nounsummer solstice, nounsummertime, nounsummery, adjectiveSun., Sunday, nounsundown, nounsunrise, nounsunset, nounsun-up, nountercentenary, nounThanksgiving, nounthirty, numberThursday, nountime, nountime, verbtimepiece, nountimer, nountime signal, nountime warp, nountime zone, nountoday, adverbtoday, nountomorrow, adverbtomorrow, nountonight, adverbtonight, nountriennial, adjectiveTuesday, nountwilight, nounWed., Wednesday, nounweek, nounweekday, nounweekend, nounweekly, adjectiveweeknight, nounWhit, nounWhitsun, nounwinter, nounwintertime, nounwk., wristwatch, nounyear, nounyesterday, adverbyr., Yule, nounYuletide, noun