Tranquil comes from the Latin root word "tranquillus," meaning "quiet, calm, still,". It transformed into the Old French word "tranquillite," meaning "peace" or "happiness".  That then evolved further into the Middle English "tranquillite," also meaning "peace" 

The earliest known use of the word "tranquil" in English is from the Middle English period around 1150-1500.  Specifically, the Oxford English Dictionary cites a translation by John Tiptoft, administrator and humanist, in 1481 as the earliest evidence. 
Tranquil in American English is an adjective meaning calm, quiet, and peaceful. 
Tranquil in British English is a noun meaning a state of calm or quietude. 

Examples of calm used in a sentence: 
"The hotel is in a tranquil rural setting. A spasm of pain crossed his normally tranquil features."
"She stared at the tranquil surface of the water."
"I am so tranquil and happy now." 
"The meadow was a tranquil site, far removed from main roads of present day habitation."
"I am going to bed with a happy and tranquil mind."
"His private life was tranquil and happy."
"From that time onward his reign was tranquil and prosperous." 

5 hours ago, drpaladin said:

Tranquil? The server made us miss the tranquil bus today.

And it made me have to recreate the entry you see above, so I'm not exactly tranquil at the moment. 

Just the facts:

TRANQUIL Definition & Meaning - Merriam-Webster

3 hours ago, Bill W said:

And it made me have to recreate the entry you see above, so I'm not exactly tranquil at the moment. 

I totally agree with you, but mine was much easier to redo.

I am really glad that the glitch did not seem to damage the site???🤞

I consider myself very lucky today. I stopped by the site this evening (as luck would have it) and saw the 'Giant Red Glitch Banner'.

If I had not, MDBCs blog streak from July 2021 would have come to a crashing end. So, yes  I consider myself to be a very lucky S.O.B.!