"With" or "Together"
* Concur: To agree
* Connect: To join together
* Confront: To face directly
* Confer: To discuss
* Congregate: To gather together
"Against" or "Opposition"
* Contradict: To say the opposite
* Contrary: Opposing
* Contest: To challenge
* Confrontation: A direct clash
* Counterfeit: A fake or imitation
"Completely" or "Thoroughly"
* Conclude: To finish
* Convince: To persuade completely
* Consume: To eat or drink completely
* Condemn: To criticize severely
* Confiscate: To seize completely
Other Meanings
* Consecutive: Following one after the other
* Conscious: Aware
* Consider: To think about carefully
* Consequence: A result or effect
* Convert: To change something into something else
This is just a small sample of the many words that start with "con." The prefix is quite versatile and can have many different meanings depending on the word.