• Doctor Syn, a character in novels by Russell Thorndike
• Grand Admiral Peccati Syn character in the Star Wars expanded universe
• Syn (goddess), in Norse mythology
• Syn addition, in organic chemistry
• The Syn, a band formerly including bassist Chris Squire of Yes
• Syn (electronic band), Scottish David T. Dewdney's group that plays Berlin School electronic music
• Sýn, an Icelandic TV station
• Synyster Gates, the lead Guitarist for Avenged Sevonfold

SYN may refer to:

• SYN (TCP), synchronise packet in transmission control protocol (TCP)
• Synchronous idle, control character in the C0 set
• The Coalition of the Left of Movements and Ecology or Synaspismos, a Greek radical left political party
• Student Youth Network, a youth media organization based in Melbourne, Australia
• Socialist Youth Network, the youth section of the Labour Representation Committee