\ˈäs \
plural ossa\ ˈä-​sə \

Definition of os 

(Entry 1 of 4)

: bone

\ˈōs \
plural ora\ ˈȯr-​ə \

Definition of os (Entry 2 of 4)

Os

symbol

Definition of Os (Entry 3 of 4)

osmium

Definition of OS (Entry 4 of 4)

1 [ Latin oculus sinister ] left eye

2 Old Style

3 operating system

4 out of stock

First Known Use of os

Noun (1)

15th century, in the meaning defined above

Noun (2)

1737, in the meaning defined above

History and Etymology for os

Noun (1)

Latin oss-, os — more at osseous

Noun (2)

Latin or-, os — more at oral

Keep scrolling for more

Learn More about os

Dictionary Entries near os

Oryzorictes

orzo

Os

os

OS

Osage

Osage orange

Statistics for os

Look-up Popularity

Time Traveler for os

The first known use of os was in the 15th century

See more words from the same century

Keep scrolling for more

More Definitions for os

os

noun
\ˈäs \
plural ossa\ ˈäs-​ə \

Medical Definition of os 

(Entry 1 of 4)

: bone — see os calcis, os coxae

os

noun
\ˈōs \
plural ora\ ˈōr-​ə, ˈȯr-​ə \

Medical Definition of os (Entry 2 of 4)

Os

symbol

Medical Definition of Os (Entry 3 of 4)

osmium

Medical Definition of OS (Entry 4 of 4)

left eye used in writing prescriptions

History and Etymology for os

Abbreviation

Latin oculus sinister

Keep scrolling for more

More from Merriam-Webster on os

See words that rhyme with os

Spanish Central: Translation of os

Nglish: Translation of os for Spanish Speakers

Comments on os

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

WORD OF THE DAY

something that serves to warn or remind

Get Word of the Day daily email!

Test Your Vocabulary

Autumn Words of the Day 2018

  • a-top-down-image-of-road-through-an-autumn-forest
  • Which is a synonym of fugacious?
How Strong Is Your Vocabulary?

Test your vocabulary with our 10-question quiz!

TAKE THE QUIZ
Word Winder's CrossWinder

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

TAKE THE QUIZ

Love words? Need even more definitions?

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