“Uroporphyrinogen.” Merriam-Webster.com Medical Dictionary, Merriam-Webster, https://www.merriam-webster.com/medical/uroporphyrinogen. Accessed 30 Nov. 2022.
Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!
See Definitions and Examples »
Get Word of the Day daily email!
Commonly Confused Words Quiz
Test your vocabulary with our 10-question quiz!
A daily challenge for crossword fanatics.
When each letter can be seen but not heard
Some may be more useful than others.
One L or two?
Look up any year to find out
How to use a word that (literally) drives some pe...
Or both? Or neither?
Editor Emily Brewster clarifies the difference.
An old-fashioned rule we can no longer put up with.
See if you can tell the insults from the complime...
Take the quiz
20 questions to help you score 1600
Can you outdo past winners of the National Spelli...