SINCE 1828

An Encyclopædia Britannica Company

Medical Dictionary

Hr factor

noun \ ˈā-ˈchär- \

medical Definition of Hr factor

: a substance present in Rh-negative blood and apparently reciprocally related to the Rh factor

Seen and Heard

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

show

WORD OF THE DAY

mollycoddle

play

to treat with excessive attention

Words at Play

All the Hits

8 obscure words for bodily harm

alt-5adf93a49b0b2

The Fossil Encased in "Case In Point"

"In point" only lives in this phrase.

alt-5adf5d017e6bf

‘Sleight’ or ‘Slight’ of Hand?

Watch closely and be amazed.

alt-5ade0f1ca7a0c

'Complement' vs. 'Compliment'

The distinction is clear (now).

Ask the Editors

2017 Word of the Year: Behind the Scenes

How we chose 'feminism'

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'

video-literally

Literally

How to use a word that (literally) drives some people nuts.

video-his-or-her

Is Singular 'They' a Better Choice?

The awkward case of 'his or her'

Word Games

rain-on-rainbow-umbrella

April 2018 Words of the Day Quiz

The rhyming verb edition.

Take the quiz

Odd Habits and Quirks Quiz

Test your knowledge of strange human behaviors.

Take the quiz

Name That Thing

Name That Thing

Test your visual vocabulary with our 10-question challenge!

Take the quiz

Add Diction

Build a chain of words by adding one letter at a time.

Play the game