Common words:
* synonym: a word with the same meaning as another word.
* synthesis: the combination of ideas or elements to form a whole.
* synchronize: to cause to happen at the same time.
* syndrome: a group of symptoms that occur together.
* synergy: the combined effect of two or more things that is greater than the sum of their individual effects.
Less common words:
* synapsis: the pairing of homologous chromosomes during meiosis.
* synapses: junctions between neurons that allow for communication.
* synaptic: relating to synapses.
* synaesthetic: relating to synaesthesia, a condition in which stimulation of one sense leads to experiences in another sense.
* synesthesia: a condition in which stimulation of one sense leads to experiences in another sense.
* syntactic: relating to syntax, the rules that govern the structure of sentences.
* syntactical: relating to syntax.
* syncretic: combining elements of different religions or cultures.
* syncopated: having the rhythm or beat changed so that the normally unstressed notes are accented.
Other words with "syn" in them:
* anhydrous: without water.
* asynchronous: not happening at the same time.
* antithesis: the direct opposite of something.
* dysfunctional: not functioning properly.
The prefix "syn" comes from the Greek word "syn", which means "together". So, words with this prefix usually have something to do with combining or joining things together.