According to Webster, this is the definition of a nerd: "an unstylish, unattractive, or socially inept person ; especially : one slavishly devoted to intellectual or academic pursuits ".
1 : a carnival performer often billed as a wild man whose act usually includes biting the head off a live chicken or snake
2 : a person often of an intellectual bent who is disliked
3 : an enthusiast or expert especially in a technological field or activity
I guess that makes the definition of a "nerd" very close to the third definition of a "geek", doesn't it?