Word: Uncanny

According to Wikipedia, The Uncanny is a "Freudian concept of an instance where something can be familiar, yet foreign at the same time, resulting in a feeling of it being uncomfortably strange." 

It also has a brief section at the bottom of the page describing it's etymology - or rather stating that "the word itself does not convey its actual meaning." So, although the word seems familiar to us, its meaning is unfamiliar in its context. However, in it's case, in stead of rejecting it completely (as it is simply a word and not a concept), we rely on the meaning that is familiar, regardless of whether or not it is correct.  While etymology was not Freud's exact discussion, it's a bit uncanny that the word 'uncanny' fits it's own description, even though it doesn't shut down our reasoning. 

http://en.wikipedia.org/wiki/The_Uncanny