Word Origins:
"diseased, sickly," from

1580s, meaning "full of cracks or flaws" 
1610s, that of "of unsound mind, or behaving as so" [krey-zee]adjective, -zi·er, -zi·est; noun, plural -zies.

1. mentally deranged; demented; insane.

2. senseless; impractical; totally unsound: a crazy scheme.

3. Informal . intensely enthusiastic; passionately excited: crazy about baseball.

4. Informal . very enamored or infatuated (usually fol. by about ): He was crazy about her.

5. Informal . intensely anxious or eager; impatient: I'm crazy to try those new skis.

6. Informal . unusual; bizarre; singular: She always wears a crazy hat.

7. Slang . wonderful; excellent; perfect: That's crazy, man, crazy.

8. likely to break or fall to pieces.

9. weak, infirm, or sickly.

10. having an unusual, unexpected, or random quality, behavior, result, pattern, etc.: a crazyreel that spins in either direction.

11. Slang . an unpredictable, nonconforming person; oddball: a house full of crazies who wear weird clothes and come in at all hours.

12. the crazies, Slang . a sense of extreme unease, nervousness, or panic; extreme jitters: The crew was starting to get the crazies from being cooped up belowdecks for so long.

Sources I used for origins and definition:
"crazy." Online Etymology Dictionary. Douglas Harper, Historian. 14 Dec. 2010. <>. 
 "crazy." Unabridged. Random House, Inc. 14 Dec. 2010. <>.