• caisson •
Pronunciation: kay-sên, kay-sahn • Hear it!
Part of Speech: Noun
Meaning: 1. A camel: an underwater compartment pumped free of water used to raise sunken objects or to work on bridge foundations. 2. A chest or container for ammunition or other explosives. 3. A horse-drawn wagon formerly used to carry ammunition but currently used to carry coffins at military funerals.
Notes: The spelling of today's word is odd because it was borrowed from French rather recently (around 1700) and has retained its French spelling. Remember the silent I and double S when you spell it.
In Play: 
The shift in meaning of today's Good Word has had an ironic effect on the famous Army song, "The Caissons Go Rolling Along":
Over hill, over dale
As we hit the dusty trail,
And the caissons go rolling along.
This word has always been indirectly associated with death, but today it is almost exclusively used with that reference: "The nation mourned as the caisson bearing the body of President Kennedy passed across our television screens." Of course, should you ever lay a foundation below water level, you will need the other type of caisson: "Architects learned a lot about caisson safety from the building of the Brooklyn Bridge."
Word History: The meanings above are ordered chronologically to show how the sense of today's word wandered from an underwater box to a carriage for a coffin. Caisson "large box" is an augmentative of French caisse "cash box", from which English also gets its word cash. Caisse is the French form of Latin capsa "box, case", a noun derived from capere "to take, hold", whose root also underlies capture and captivate. 
The original Proto-Indo-European root developed into German haben and English have, since the PIE [k] sound developed into English [h] in initial position and [gh] elsewhere in words. All these words are things that hold or are held. (Today we are beholden to Chris Berry for suggesting we write up this captivating word.)
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