Sy is a given name, nickname/hypocorism (often of Seymour) and surname which may refer to:
Sydney ( ( listen)) is the state capital of New South Wales and the most populous city in Australia and Oceania.
The Klyntar (colloquial: Symbiotes) are a fictional species of inorganic, amorphous extraterrestrial symbiotes appearing in American comic books published by Marvel Comics.
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.
Synesthesia 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.
A synthesizer (often abbreviated as synth) is an electronic musical instrument that generates audio signals that may be converted to sound.
Roger Keith "Syd" Barrett (6 January 1946 – 7 July 2006) was an English singer, songwriter, and musician.