Upsilon/ˈʊpsɪlɑːn/ Definition 1 of 2Pro Tip 1/3Greek Origin Remember that 'upsilon' is specific to the Greek language and culture. The Greek word 'Υγεία' (health) starts with an upsilon. Pro Tip 2/3Pronunciation 'Upsilon' in Greek has a sound similar to the French 'u' or the German 'ü'. You pronounce 'upsilon' differently than 'u' in English. Pro Tip 3/3Not a 'Y' Don't confuse 'upsilon' with the English 'Y', although it looks similar. Greek upsilon is related to Y, but they aren't the same letter.