You use these words on a regular basis, but their etymology may surprise you.
Addict
Under ancient Roman law, addiction referred to the legal surrendering of an individual as a slave to a master. Ultimately, the term addict became associated with habitual behavior that made a person a slave to something else; this included the craving of substances such as drugs or alcohol.
Source: gutenberg.org
Carat
Carat, the standard unit of weight for precious stones, derives from the Greek word for carob seeds, "keraton." Apparently, fully grown carob seeds have a consistent weight from seed to seed (approximately 200mg), which made them a handy item to determine the weight of small objects, such as diamonds, on a balance scale.
Via: belocal.de
Cell
After examining plant matter under a microscope, early modern scientist Robert Hooke coined the word cell to refer to the smallest unit of life because plants' cellular structure resembled monks' cells (living quarters) in a monastery.
Via: flickr.com
Ketchup
Although we commonly think of ketchup as a tomato product, historically the term derives from a Chinese fish sauce called ke-tsiap. English travelers likely brought the recipe back from Malaysia. By the mid-eighteenth century, "ketchup" or "catsup" was a common staple in Britain and its American colonies. Tomatoes weren't part of the recipe until the 1790s, partly due to a common English/American belief that tomatoes were unsuitable for human consumption.