The Origin of Upsilon in Greek Loan Words

Upsilon was used as both a vowel and also for the consonant wuh or W sound at the front of a syllable. The top part of Upsilon became our letter U, written with either two straight lines or one curvy line. Now we need to jump forward a bit to the Anglo-Saxon period to see how those letters were applied to old English. Think about all of those words that begin with S-Y like system, syllable, and sympathy. They're all Greek words, or based on Greek roots. We spell the vowel sound in those words with a Y instead of an I because that's the way the Greeks spelled them.