crackpot

Short definition from Wiktionary

Noun

1. 1
   An eccentric, crazy or foolish person.
2. 2
   Someone addicted to crack cocaine (i.e. a drug addict).

Adjective

1. 1
   Eccentric or impractical.

Proper noun

1. 1
   A small village in Grinton parish, Swaledale, North Yorkshire, England, previously in Richmondshire district (OS grid ref SD9796)