Definition of mesothorium
: either of two radioactive products intermediate between thorium and radiothorium in the thorium series or a mixture of the two products obtained usually from thorium minerals (as monazite sand) and used as a substitute for radium especially in luminous paints: a : an isotope of radium —called also mesothorium 1 —symbol MsTh1 or Ra228 b : an isotope of actinium —called also mesothorium 2 —symbol MsTh2 or Ac228
Love words? 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:
- More than 250,000 words that aren't in our free dictionary
- Expanded definitions, etymologies, and usage notes
- Advanced search features
- Ad free!
Origin and Etymology of mesothorium
New Latin, from mes- + thorium
Seen and Heard
What made you want to look up mesothorium? Please tell us where you read or heard it (including the quote, if possible).