photoperiodism

noun

pho·​to·​pe·​ri·​od·​ism ˌfō-tō-ˈpir-ē-ə-ˌdi-zəm How to pronounce photoperiodism (audio)
: a plant's or animal's response or capacity to respond to photoperiod

Word History

First Known Use

circa 1911, in the meaning defined above

Time Traveler
The first known use of photoperiodism was circa 1911

Rhymes for photoperiodism

See All Rhymes for photoperiodism

Browse Nearby Words

photoperiod
photoperiodism
photophase
See all Nearby Words

Cite this Entry

“Photoperiodism.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/photoperiodism. Accessed 7 Jul. 2026.

Copy Citation

Medical Definition

photoperiodism

noun
pho·​to·​pe·​ri·​od·​ism -ˈpir-ē-ə-ˌdiz-əm How to pronounce photoperiodism (audio)
variants also photoperiodicity
-ˌpir-ē-ə-ˈdis-ət-ē How to pronounce photoperiodism (audio)
plural photoperiodisms also photoperiodities
: the response or the capacity to respond to photoperiod

More from Merriam-Webster on photoperiodism

Britannica.com: Encyclopedia article about photoperiodism

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

Popular in Grammar & Usage

See More

Is that lie 'bald-faced' or 'bold-faced'?

'A' or 'an'? What about before 'h'? An Indefinite Article Guide

Why is '-ed' sometimes pronounced at the end of a word?

Commonly Misspelled Words

How to Use Em Dashes (—), En Dashes (–) , and Hyphens (-)
See More

Popular in Wordplay

See More

14 Phobias You Probably Haven't Heard Of

The Longest Long Words List

One-Word Oxymorons: Bittersweet, Spendthrift, and More

Ten Words Ending with a Silent ‘T’

12 Lovely and Unusual Words for the Natural World
See More

Popular

See More

Is that lie 'bald-faced' or 'bold-faced'?

14 Phobias You Probably Haven't Heard Of

The Longest Long Words List
See More

Games & Quizzes

See All
Play Quordle: Guess all four words in a limited number of tries. Each of your guesses must be a real 5-letter word.
Quordle Can you solve 4 words at once?
Play Blossom: Solve today's spelling word game by finding as many words as you can using just 7 letters. Longer words score more points.
Blossom Pick the best words!
Play Missing Letter: a crossword with a twist. Each of the 25 puzzle words start with a different letter of the alphabet. Which letter is missing?
The Missing Letter A daily crossword with a twist
hangman letters and game
Hangman Lightning Round Figure out which word fits in the blanks.
See All