Definition of black helicopter in English:

black helicopter

noun

US
  • (In the context of various conspiracy theories) an unmarked, dark-coloured helicopter believed to be involved in sinister or covert activities, especially relating to the establishment of a global government.

adjective

US
  • (attributive) of or relating to belief in conspiracies of this type.

Origin

1970s; earliest use found in Havre (Montana) Daily News.