little green man

noun4

1. •
   A conventional fictional alien from outer space in the form of a small humanoid with green skin.

   • An engram is NOT [...] One of the little green men Americans claim have crashed in flying saucers. — 1950
2. •
   (humorous) One of the supposed extraterrestrial occupants of a UFO.
3. •
   [usually plural] (euphemistic) A soldier (wearing green military fatigues) without identification in order to create an air of uncertainty around their allegiance.
4. •
   A type of diminutive sprite or fairy that wears green clothing.

   • It was the pantomime of "Jack and the Bean Stalk," and as the Hallicots entered a large number of little green men were hammering on anvils in a gloomy and spacious cave. — 1866