mong /ˈmʌŋ/noun 3/mɒŋ/ noun 2forms 1phrases 1 noun3 •(Australia, slang) A mongrel dog. •(dialect) A mingling, mixture, or crowd. •(dialect) A muddle or confusion. mong /mɒŋ/ noun2 •(slang, offensive) A stupid person.Can't you see you don't belong / You're a stupid little fucking mong — 2016 •(slang, offensive) A person with Down's syndrome. formsmongs Phrases with mong mong outTo be tired, stupid, lazy or freaked out due to being stoned or intoxicated.