615. coeval : living at the same time as; contemporary

　　* coeval with the dinosaur, the pterodactyl flourished during the Mesozoic era.

　　617. cogent : convincing

　　* She presented cogent arguments to the jury.

　　618. cogitate : think over

　　* cogitate on this problem; the solution will come.

　　619. cognate : related linguistically; allied by blood; similar or akin in nature

　　* The English word \mother\ cognate to the Latin word \mater,\ whose influence is visible in the words \maternal\ and \maternity.\

　　620. cognitive : having to do with knowing or perceiving related to the mental precesses

　　* Though Jack was emotionally immature, his cognitive development was admirable; he was very advanced intellectually.

　　621. cognizance : knowledge

　　* During the election campaign, the two candidates were kept in full cognizance of the international situation.

　　622. cohere : stick together

　　* Solids have a greater tendency to cohere than liquids.

　　623. cohesion : tendency to keep together

　　* A firm believer in the maxim \Divide and conquer,\ the emperor, by lies and trickery, sought to disrupt the cohesion of the free nations.

　　626. coincident : occurring at the same time

　　* Some people find the coincident events in Hardy's novels annoyingly improbable.

　　628. collaborate : work together

　　* Two writers collaborated in preparing this book.

　　630. collate : examine in order to verify authenticity; arrange in order

　　* They collated the newly found manuscripts to determine their age.

　　631. collateral : security given for loan

　　* The sum you wish to borrow is so large that it must be secured by collateral.

　　633. colloquial : pertaining to conversational or common speech

　　* Your use of colloquial expressions in a formal essay such as the one you have presented spoils the effect you hope to achieve.

　　634. colloquy : informal discussion

　　* I enjoy our colloquies but I sometimes wish that they could be made more formal and more searching.

　　635. collusion : conspiring in a fraudulent scheme

　　* The swindlers were found guilty of collusion.

　　646. commensurate : equal in extent

　　* Your reward will be commensurate with your effort.