1
general::
Ruthless acquisition or competition, as in With shrinking markets, it's dog eat dog for every company in this field. This contradicts a Latin proverb which maintains that dog does not eat dog, first recorded in English in 1543. Nevertheless, by 1732 it was put as "Dogs are hard drove when they eat dogs" (Thomas Fuller, Gnomologia).
American Heritage Idioms
2
general::
Phrase(s): dog-eat-dog
Fig. a situation in which one has to act ruthlessly in order to survive or succeed; ruthless competition. • It is dog-eat-dog in the world of business these days. • Universities are not quiet peaceful places. It’s dog-eat-dog to get a promotion.
McGrawhill's American Idioms And Phrasal Verbs