1) Crank 2) Dingdong 3) Fruitcake 4) Kooky 5) Loon 6) Lunatic 7) Maniac 8) Nut 9) Nutcase 10) Nut job 1) Crank 2) Eccentric 3) Eccentric one 4) Eccentric person 5) Erratic one, slang 6) Exclusively Saxon word 7) Exclusively Anglo word 8) Flake 9) Fruitcake 10) Geek 11) Loon 12) Lunatic 13) Nut case 14) Nutcase 15) Odd fellow 16) Oddball 17) Ridiculous 18) Screwball 19) Unrealistic one 20) Whack job 
Crackpot is British slang for mad, insane, crazy.
[n] - a whimsically eccentric person
crank 1 nut 2 nut case noun a whimsically eccentric person