Haggard

What's haggard? An adjective meaning badly dressed, exhausted, and emotionally distressed.  It's synonym is another fine word--gaunt.

And the word--improbably--comes from Old French, through German.  It meant a wild hawk, or raptor.  So how does that translate to an adjective meaning exhausted and depressed?  Your guess is as good as mine.....  

Snigger

"Stop sniggering!" my mother always directed.  So what did she mean?

To snigger is to laugh quietly and, most importantly, disrespectfully.  The word is also the a noun.

And where did it come from?  The dictionary suggests that it's an alteration of another word for the same thing--snicker.  And that word?  "Perhaps imitative"says the dictionary.  But to me, that sounds like a stretch....

Whack, out of

"Things are out of whack," said a friend.  I knew what he meant--the situation was disordered and messy.  And I knew what a whack was--it's a strong blow or strike.  But what a strange word--whack?  Where does it come from?  And why can something be out of whack but not IN whack?

The word can be traced to the 1700's, and comes into English from the Scottish.  That much I know.  But as to the rest--sorry, that's a mystery!