grass-eater

noun4

1. •
   An organism notable for eating grass
2. •
   A fish of species Distichodus rostratus or Distichodus engycephalus, of Africa
3. •
   (slang, offensive) A celibate man, especially a Japanese man, who eschews dating and sexual relationships.

   • That is what the modern men of Japan have done, these grass-eaters. — 2011
4. •
   (figurative) A police officer who accepts offered bribes but does not actively seek them out.

   • But why do police become grass-eaters at all, if they lack the greed and contempt fo decency necessary to become meat-eaters? — 2002