This can be interpreted several ways.
Synopen as just a name derived from syndication that doesn't have to have any real meaning.
SynOpen for open syndication
SynoPen which I think of as Synthesis via Pen, nonsense yes, but kind of a creation via writing angle.
No trademarks match.
Google returns 68 results, no obvious conflicts
synopen.com/net/org all available.
display sample icons here
[AsbjornUlsberg] What about just calling it Synopsis? I think the words Publish and Syndicate in all their forms are over-used and boring. SynOpsis (with a capital O) could probably be an alternative.