Sy is a given name, nickname/hypocorism (often of Seymour) and surname which may refer to:
Systemic lupus erythematosus (SLE), also known simply as lupus, is an autoimmune disease in which the body's immune system mistakenly attacks healthy tissue in many parts of the body.
Sydney () is the state capital of New South Wales and the most populous city in Australia and Oceania.
Synesthesia (also spelled synæsthesia or synaesthesia; from the Ancient Greek σύν syn, "together", and αἴσθησις aisthēsis, "sensation") is a perceptual phenomenon in which stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway.
Michael Sylvester "Sly" Gardenzio Stallone (; Italian: [stalˈloːne]; born July 6, 1946) is an American actor and filmmaker.
A synthesizer (often abbreviated as synth, also spelled synthesiser) is an electronic musical instrument that generates electric signals that are converted to sound through instrument amplifiers and loudspeakers or headphones.
Roger Keith "Syd" Barrett (6 January 1946 – 7 July 2006) was an English musician, composer, singer-songwriter, and painter.