Why does the back of your lower leg have the same name as a baby cow? How come the bottom of your foot has the name of a fish?
This one’s a coincidence. The baby cow calf and the back of the lower leg calf are homographs, words with different origins that ended up spelled (and in this case pronounced) the same. The bovine word is from Old English cælf, of Germanic origin. The anatomical term entered English in the Middle Ages and comes from Old Norse kálfi.
On the other hand (or should we say the other foot?), the fishy and the fleshy sole are related. Sole, meaning the bottom of a person’s foot, entered Middle English via Old French, from Latin solea, meaning "sandal, sill," which is derived from solum, meaning "bottom," "pavement," or—wait for it—"sole." The fish is named for its shape: like the bottom of a foot.
What does the inner surface of your hand have to do with trees you might see on a beach in Hawaii? Tropical islands aren’t the only places with palm trees. In ancient Rome it was customary to place a palm leaf in the hands of the victor in a contest. The Latin word palma (also palmus), meaning "palm of the hand," became associated with the tree. Fun fact: the Romans also used palma for the underside of a webbed foot.
If you guessed that the –bow in elbow has to do with bending (even if it’s not bending into a smooth arc like a rainbow or a cross-bow), you’re right. But what about the el-? Old English ęln, meaning "arm or forearm," is related to ulna, which meant the same in Latin, and is now used in English to refer to the large inner bone of the forearm. El- is also related to ell, the unit of length sometimes defined as the distance from the elbow to the wrist, which is probably the source of much arm-wrestling between long-armed customers and short-armed cloth merchants.
The word for the short, thick, opposable digit of the human hand goes back to Old English thūma, from the Indo-European root teuə-, "to swell." Other words derived from this root are thigh, thousand, thimble, tumor, butter, tomb, and tumescence. Keep that in mind when you give someone the old “thumbs up.”
6. Index finger
This digit wasn’t named for its usefulness in flipping to the end of a book to look something up, but because it’s used for pointing or indicating. In fact the earliest meaning (from the late 1300s) of index is "the forefinger." The use of the word to mean "an alphabetical list pointing to occurrences of names or subjects within a book" came a couple of centuries later.
What does the opening in the eye that allows light to reach the retina have to do with a young student? Pupil, originally meaning "orphan" or "ward," came into late Middle English from Old French pupille, which derives from Latin pupillus (diminutive of pupus, "boy") and pupilla (diminutive of pupa, "girl"). By the 16th century, it came to mean "a person who is being taught by another." The pupil of the eye also came into late Middle English from Old French pupille, likewise from Latin pupilla, with the extended sense of "doll" rather than "little girl." Why a doll? Believe it or not, lexicographers claim it’s because of the small, reflected image you see when looking into someone’s pupil.
Speaking of the eye, why does its colored part have the name of a flower? The colorful ring-shaped membrane of the eye and the flower both take their name from Iris, the goddess of the rainbow in Greek mythology.
Thanks to Laura Herman and Gene Herman for asking the questions that inspired this list.
Sources: OED [Oxford English Dictionary] Online, New Oxford American Dictionary (Second Ed.), The American Heritage Dictionary of the English Language (Fifth ed.)