Definition of junkyard dog in English:

junkyard dog

Pronunciation /ˌdʒʌŋkjɑːd ˈdɒɡ/

noun

US
  • 1A watchdog which guards a junkyard; in later use chiefly in comparisons and similes denoting an aggressive animal or person, with reference to junkyard watchdogs' reputation for viciousness.

  • 2An aggressive, ruthless, or tenacious person, especially a lawyer or government official.

Origin

1930s. From junkyard + dog.