upsilon /ūp-sīˈlon, ŭp-, ūpˈsi- or upˈsi-/ or ypsilon /ip-sīˈlon or ipˈsi-/

1. The twentieth letter of the Greek alphabet (Υ, υ)
2. As a numeral υˈ = 400, ˌυ = 400000
3. A short-lived heavy subatomic particle produced when beryllium nuclei are bombarded with high-energy protons

• arts centre
• arts centres
• artsier
• artsies
• artsiest
• artsman
• artsmen
• art-song
• art-songs
• artsy
• artsy-fartsy
• art therapy
• art union
• artwork
• artworks
• arty
• arty-crafty
• arty-farty
• arugula
• arugulas
• arum
• arum lilies
• arum lily
• arums
• arundinaceous