Language Of Confusion: Tense, Part IV

Still more words from the Proto Indo European root ten-, to stretch. Appropriate, as these definitions are definitely a stretch.
 
The first word we’re looking at today is hypotenuse, as in the leg of a triangle across from the right angle. It showed up in the late sixteenth century from the Late Latin hypotenusa, from the Greek hypoteinousa. That’s a mix of hypo-, which means under, and teinein, to stretch, which is from the PIE ten-. A hypotenuse stretches under—or across—from a right angle.
 
Next is the last word to actually have ten in it: lieutenant. Really! It showed up in the late fourteenth century meaning one who takes the place of another—it wasn’t a rank until a century later. It’s from the Old French lieu tenant, which means substitute or deputy, with lieu meaning place (as in, in lieu of) and tenant from the verb tenir, to hold, which is from ten-, to stretch. Now, the rank notion is that a lieutenant is the one taking the place of the captain in their absence, so the lieu part makes sense. It’s the ten part that’s weird. A lieutenant stretches in the place of a captain?
 
Also from ten- is temple—temple like the side of your forehead, as a place of worship temple might not actually be related. Forehead temple showed up in the mid fourteenth century from the Old French temple, Vulgar Latin tempula, and classical Latin tempora, meaning side of the forehead here. That’s from ten-, apparently in the sense that the temple is a thin stretch of skin on the side of your head. As for the other temple, that might be from ten- in the sense of one stretching in front of an altar in worship. Or it may be from the Proto Indo Eurpoean temp-, to cut, as in a place reserved (or cut out) for worship. Either way, it makes little sense.
 
The next word makes sense when you think about it: thin. It comes from the Old English þynne, thin, and making it the first word we’ve looked at from Germanic origins instead of Latin. Before English, it was the Proto Germanic thunni, which is from ten-, to stretch, because thin things can be stretched out.
 
Finally today, rein, which doesn’t even have a T in it. It showed up in the fourteenth century, from the Old French rene/resne, thought to be from the Vulgar Latin retina—no, not related to the eyeball word, it means bond or check here. That’s from the classical Latin retinere, to retain. So rein is from retain, it just lost the T. And now you know what we’ll be looking at next week.
 
Sources
Online Etymology Dictionary
Google Translate
Omniglot
University of Texas at Austin Linguistic Research Center
University of Texas at San Antonio’s page on Proto Indo European language
Tony Jebson’s page on the Origins of Old English
Old English-English Dictionary
Encyclopaedia Britannica
Orbis Latinus