General:
* Co-author: A person who writes a book, article, etc., with another person.
* Co-worker: A person who works with another person, especially at the same job.
* Co-operate: To work together for a common goal.
* Co-ordinate: To organize or arrange things in a way that they work well together.
* Co-exist: To live or exist together peacefully.
* Co-founder: One of the people who started an organization or company.
* Co-pilot: A pilot who assists the main pilot of an aircraft.
* Co-sign: To add your signature to a document along with someone else.
* Co-star: To act in a film or play with another actor.
* Co-efficient: A number that multiplies a variable in an algebraic expression.
More Specific:
* Co-dependent: Relating to a relationship where two people rely on each other too much.
* Co-ed: Short for co-educational, referring to a school or college where boys and girls attend together.
* Co-evolution: The process of two or more species evolving together in response to each other.
* Co-habitation: Living together in a sexual relationship without being married.
* Co-insurance: A type of insurance that requires the insured to pay a percentage of the costs.
* Co-founder: One of the people who started a company or organization.
* Co-founder: One of the people who started a company or organization.
This is just a small sample of the many words that start with the prefix "co-." The meaning of the prefix "co-" usually indicates that two or more things are involved or working together.