SINCE 1828

An Encyclopædia Britannica Company

Medical Dictionary

tachysterol

play play

noun ta·chys·ter·ol \ta-ˈkist-ə-ˌrȯl, -ˌrōl\

Medical Definition of tachysterol

: an oily liquid alcohol C₂₈H₄₃OH isomeric with ergosterol that is formed by ultraviolet irradiation of ergosterol or lumisterol and that on further irradiation yields vitamin D₂—see dihydrotachysterol

Seen and Heard

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

show

WORD OF THE DAY

volplane

play

to glide in or as if in an airplane

Words at Play

alt-594d2b6325245

'Pride': The Word That Went From Vice to Strength

Do you take pride in Pride?

Pink: The Color that Will Change Your Life

From Fuchsia to Baker-Miller Pink

That Sucks Word Alternatives

Your day is the worst. Your vocabulary is the best.

alt-5931949575ca5

'All the Feels,' All the Time

Once more, with 'feels'

Ask the Editors

Is it wrong to use 'decimate' to mean 'destroy'?

Language changes

The Serial Comma

Why don't they call it the Merriam-Webster comma?

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

istock-refers-to-this-as-a-tumble-of-strawberries-which-sounded-pretty-nice-to-us

June 2017 Words of the Day Quiz

Summer's first WOTD quiz.

Take the quiz

alt-5941ad7527c3c

Yearbook Superlatives Quiz

Is that your picture under "Largest Vocabulary"?

Take the quiz

Name That Thing

Name That Thing

Test your visual vocabulary with our 10-question challenge!

Take the quiz

Dictionary Devil

Dictionary Devil

The dictionary has been scrambled—can you put it back together?

Play the game