SINCE 1828

An Encyclopædia Britannica Company

vitamin D

noun

Definition of vitamin D

:any or all of several fat-soluble vitamins chemically related to steroids, essential for normal bone and tooth structure, and found especially in fish-liver oils, egg yolk, and milk or produced by activation (as by ultraviolet irradiation) of sterols: such as

a or vitamin D₂ play \-ˈdē-ˈtü\ :calciferol

b or vitamin D₃ play \-ˈdē-ˈthrē\ :cholecalciferol

See vitamin D defined for kids

First Known Use of vitamin d

circa 1921

Medical Dictionary

vitamin D

noun

medical Definition of vitamin D

:any or all of several fat-soluble vitamins chemically related to steroids, essential for normal bone and tooth structure, and found especially in fish-liver oils, egg yolk, and milk or produced by activation (as by ultraviolet irradiation) of sterols: as

a :calciferol

b :cholecalciferol — called also sunshine vitamin

Learn More about vitamin d

Britannica.com: Encyclopedia article about vitamin D

Seen and Heard

What made you want to look up vitamin D? Please tell us where you read or heard it (including the quote, if possible).

show

WORD OF THE DAY

yeasty

play

of yeast or being unsettled or frivolous

BROWSE DICTIONARY

vitamin B complex

vitamin C

vitamin D

vitamin E

vitamined

Test Your Vocabulary

Merriam-Webster's New Words Quiz—Fall 2017 Edition!

Which of the following is a new sense of the word bunny?

Name That Thing

Test your visual vocabulary with our 10-question challenge!

TAKE THE QUIZ

Word Winder's CrossWinder

Test Your Knowledge - and learn some interesting things along the way.

TAKE THE QUIZ

Words at Play

alt-59c4207ecf106

Let's Talk 'Tea'

Spill it, sip it: just make it hot.

8 Words and Phrases from Boxing and Wrestling

Common terms that come from boxing and wrestling

alt-59c2960017c94

The Ambiguity of Pushing 'Up' and 'Back'

When you push a meeting, where does it go?

Silent Letters

When each letter can be seen but not heard

Ask the Editors

video-title-words-of-the-year-1066

Words of the Year: 1066

Or, Why Pig Meat is Called 'Pork' and Cow Meat is Called 'Beef'

How Often Is 'Biweekly'?

Don't get us started on 'bimonthly'

video-irregardless-grammar-peeve-blend-of-the-synonyms-irrespective-and-regardless

Irregardless

It is in fact a real word (but that doesn't mean you should use it).

video-moose-goose-weird-plurals

Weird Plurals

One goose, two geese. One moose, two... moose. What's up with that?

Word Games

young-plant-shoots

Merriam-Webster's New Words Quiz—Fall 2017 Edition!

You're going to have to memorize the dictionary again.

Take the quiz

stylized-drawing-of-woman-pole-vaulting-across-gap-to-get-trophy

Challenging Vocabulary Quiz Returns!

No tricks, just difficult words.

Take the quiz

Name That Thing

Name That Thing

Test your visual vocabulary with our 10-question challenge!

Take the quiz

Word Winder's CrossWinder

Word Winder's CrossWinder

A game of winding words.

Play the game