By - Monke-Mammoth
Huge differences but sometimes compatible, but I'm not a big theory dude, I'll summarise my understanding: Anarcho-Syndicalism refers to the use of militant unions as the primary vehicle of liberation. So worker organisation into unions along anarchist principles, with the intention of the unions taking over and managing the workplace. Anarcho-communism is perhaps a broader set of ideals that refer to an anarchist state of affairs without private property - which I'd say is the key concept in communism.In some cases anarcho-syndicalists will advocate for some aspects of marketised production which some communists would disagree with. However you could also take a radical approach to anarcho-syndicalism and confederate the syndicates/workplaces eventually leading to a communist needs based distribution system that replaces a market.
I think your comment brings out the two dimensions of these isms, the practical theory and the end-state theory. Roughly put, the first is a theory about what we should do now and in the short term. The second is a theory about how society should look. I take a-s to be a practical theory that differs from a-c, but it seems to me like they will be basically the same end-state theory.
Syndicalism comes from the French word for trade union and us anarcho-syndicalists advocate for using trade unions as a way of organising an anarchist society. Distributing resources, organising democratic workplaces and direct democracy etc.
Communists want a moneyless society in which resources are distributed through the communist principle of "each according to his ability to each according to his need" which makes currency obsolete.
There are loooots of other differences but these are the main ones imo