rain man

noun5

1. •
   (offensive) An autistic, or mentally and/or socially impaired person.
2. •
   (offensive) A non-autistic or impaired person whose mannerisms are similar to such people.
3. •
   (humorous) An expert at something.

   • David Milarch calls him the “rain man of trees” because of his brilliance with tree data and his uncanny knack for finding the big ones. — 2013
4. •
   A man who is believed to have power to control the rain.

   • We believe that if we want rain, the rain man of the tribe must imitate the rain by squirting water from his mouth, and the painters must retrace the age-old paintings at the cave of the water totem. — 1978
5. •
   A spirit of the rain.

   • These depict in vivid descriptions how the rain man in the west expands in the form of a black cloud; white clouds precede him which unfold like a flower — 2009