There are some words which change their meaning over time but leave behind a footprint of their former senses in expressions and compound words. A great example of this is quick.
Nowadays, quick means ‘fast’ but this was not always the case. The word is of Germanic origin with the original form being cwic or cwicu and it meant ‘alive, animated’. In fact, it has an Indo-European root *gweie-, which also gave the Latin vivus and the Greek bios.
The original sense of the word does still exist now but only in set phrases like the quick and the dead and the fact that the quick and the dead is often misinterpreted with the ‘fast’ meaning shows how outdated the ‘living’ meaning is.
Other words which still contain the former meaning are quicksilver and quicklime: quicksilver, another term for mercury, is supposedly ‘alive’ because of the way the drops of liquid mercury move; quicklime is so called because of its vigorousness and is a direct translation from the Latin calx viva.
In around 1300, quick went from meaning ‘alive’ to ‘moving, shifting’ and it is this meaning which lead to quicksand. Much to Hollywood’s dismay, quicksand is not fast at all, but just moving. In reality, it is almost impossible to sink all the way into quicksand since it is rarely more than a few feet deep. What’s more, you’ll only sink quickly if you panic and struggle. Keep calm, move slowly and, since your body is less dense than quicksand, you’ll eventually get out, which goes to show etymology is not only interesting, but useful in survival situations too.