It comes from the Greek word "syn", which has the same meaning.
Here are some examples of words with the prefix "syn-":
* synthesis: the combination of ideas or parts to form a whole
* synchronize: to cause to happen at the same time
* synergy: the interaction of two or more agents or forces so that their combined effect is greater than the sum of their individual effects
* synopsis: a brief summary of the main points of something
* synonym: a word having the same or nearly the same meaning as another word