[bahy-en-ee-uh l]
adjective Also biyearly (for defs 1, 2).
  1. happening every two years: biennial games.
  2. lasting or enduring for two years: a biennial life cycle.
  3. Botany. completing its normal term of life in two years, flowering and fruiting the second year, as beets or winter wheat.
  1. any event occurring once in two years.
  2. Botany. a biennial plant.

Origin of biennial

First recorded in 1615–25; bienni(um) + -al1
Related formsbi·en·ni·al·ly, adverb
Can be confusedbiannual biennial semiannual (see usage note at bi-1)

Usage note

See bi-1. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for biennially

Historical Examples of biennially

  • In some states the legislatures meet annually; in others, biennially.

    Why We Punctuate

    William Livingston Klein

  • Time of meeting of the legislature, fourth Monday in November, biennially.

    The South-West

    Jonathon Holt Ingraham

  • This body meets in August, biennially, to revise the jury list.

    Elements of Civil Government

    Alexander L. Peterman

  • Legislature and State officers elected quadrennially; members Congress, biennially.

  • Some unions meet annually, some biennially, some triennially, and a few determine by referendum when the convention is to meet.

    The Armies of Labor

    Samuel P. Orth

British Dictionary definitions for biennially


  1. occurring every two years
  2. lasting two yearsCompare biannual
  1. a plant, such as the carrot, that completes its life cycle within two years, developing vegetative storage parts during the first year and flowering and fruiting in its second yearCompare annual (def. 3), perennial (def. 3)
  2. an event that takes place every two years
Derived Formsbiennially, adverb
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for biennially



"lasting for two years" (1620s); "occurring every two years" (1750), from Latin biennium "two-year period," from bi- (see bi-) + annus "year" (see annual). The vowel change is "due to the Latin phonetic law according to which the unaccented and closed radical syllable of the second element of compounds, original -ă- becomes -ĕ-" [Klein]. The noun meaning "a biennial plant" is attested by 1770.

Online Etymology Dictionary, © 2010 Douglas Harper

biennially in Science


  1. Completing a life cycle normally in two growing seasons.
  1. A biennial plant. In the first year, biennials normally produce a short stem, a rosette of leaves, and a fleshy root that acts as food supply. In the second season, biennials blossom, produce seed, use up their food supply, and die. Carrots, parsnips, and sugar beets are examples of biennials. Compare annual perennial.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.