The definition of dog eat dog is something or some situation in which there is fierce, ruthless competition.
(adjective)An example of dog eat dog is a competitive sales environment where everyone is trying to beat out their co-workers to make the most sales, even if they have to lie and cheat to do it.
See dog-eat-dog in Webster's New World College Dictionary
adjective
See dog-eat-dog in American Heritage Dictionary 4
adjective
Learn more about dog-eat-dog