Definition of upsilon
1
: the 20th letter of the Greek alphabet — see Alphabet Table
2
: any of a group of unstable electrically neutral elementary particles of the meson family that have a mass about 10 times that of a proton
Test Your Vocabulary
Eponyms: Words Named After People
-
- What is the best definition of boycott?

Test your visual vocabulary with our 10-question challenge!
TAKE THE QUIZ
A daily challenge for crossword fanatics.
TAKE THE QUIZLove words? Need even more definitions?
Merriam-Webster unabridged
Share upsilon
Time Traveler for upsilon
The first known use of upsilon was in 1621
See more words from the same year