A puzzle for philosophy professors:  Consider the statement "Some of my best friends are Jews".

When did "orthogonal" take on the meaning "irrelevant"?

Common understandings of words, though the definitions are not in the dictionary.

Irony - Signaling admission and acceptance of conflicted emotional attachments or dual loyalties. 

Subtext -The meaning of a statement that has no direct relation to its grammatical structure.

To be fair, the dictionary definition of irony did include dramatic irony...

a literary technique, originally used in Greek tragedy, by which the full significance of a character's words or actions are clear to the audience or reader although unknown to the character.... 

but with no mention of its origins in the behavior of actual people.