Syn may refer to:
- Syn (goddess), in Norse mythology
- Syn addition, in organic chemistry
- The Syn, a band formerly including bassist Chris Squire of Yes
- Sýn, an Icelandic TV station
- Doctor Syn, a character in novels by Russell Thorndike
- Grand Admiral Peccati Syn character in the Star Wars expanded universe
- Synonym (taxonomy), a system of accepted alternative names for species
- Synyster Gates, the lead guitarist for Avenged Sevenfold
- DJ Synystr
SYN may refer to:
- SYN (TCP), synchronise packet in transmission control protocol (TCP)
- Synchronous idle (␖), one of the C0 and C1 control codes
- Synaspismós, the Coalition of the Left of Movements and Ecology, a Greek radical left political party
- Student Youth Network, a youth media organization based in Melbourne, Australia
- SYN (OSC), a standardized namespace within Open Sound Control (OSC)
- SYN (band), a band by Halca (singer)