You must — there are over 200,000 words in our free online dictionary, but you are looking for one that’s only in the Merriam-Webster Unabridged Dictionary.
Start your free trial today and get unlimited access to America's largest dictionary, with:
helium + 3, mass number of the isotope
Cite this Entry
“Helium-3.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/helium-3. Accessed 6 Dec. 2021.
See Definitions and Examples »
Get Word of the Day daily email!
Farm Idioms Quiz
Can you spell these 10 commonly misspelled words?
Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!
Top 10 Latin Phrases
Don't argue with the dictionary
This is usage
A simple trick to keep them separate
How 'literally' can mean "figuratively"
How to use a word that (literally) drives some pe...
The awkward case of 'his or her'
How many do you know?
Take the quiz